diff --git a/deno.json b/deno.json
index 9fcf2d4..2ac98ed 100644
--- a/deno.json
+++ b/deno.json
@@ -1,7 +1,7 @@
 {
   "tasks": {
-    "start": "deno run --allow-read --allow-write --allow-env main.ts",
-    "dev": "deno run --watch --allow-read --allow-write --allow-env main.ts"
+    "start": "deno run --allow-read --allow-write main.ts",
+    "dev": "deno run --watch --allow-read --allow-write main.ts"
   },
   "imports": {
     "@std/path": "jsr:@std/path@^1.0.0",
diff --git a/game.ts b/game.ts
index 779fb20..5fdddb5 100644
--- a/game.ts
+++ b/game.ts
@@ -33,6 +33,11 @@ export interface GameSession {
   bestStreak: number;
 }
 
+// Constants for word filtering
+const MIN_WORD_LENGTH = 3;
+const MAX_WORD_LENGTH = 8;
+const WORD_POOL_SIZE = 500;
+
 // Character sets for different difficulty levels
 const LETTERS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".split("");
 const NUMBERS = "0123456789".split("");
@@ -40,18 +45,32 @@ const PUNCTUATION = ".,?!-/()@".split("");
 const ALPHANUMERIC = [...LETTERS, ...NUMBERS];
 const FULL_SET = [...LETTERS, ...NUMBERS, ...PUNCTUATION];
 
+/**
+ * Fisher-Yates shuffle algorithm - O(n) complexity
+ */
+function shuffleArray<T>(array: T[]): T[] {
+  const shuffled = [...array];
+  for (let i = shuffled.length - 1; i > 0; i--) {
+    const j = Math.floor(Math.random() * (i + 1));
+    [shuffled[i], shuffled[j]] = [shuffled[j], shuffled[i]];
+  }
+  return shuffled;
+}
+
 // Filter words for morse code practice (3-8 letters, common words)
 const ALL_WORDS = wordsArray
   .filter((word: string) => {
     const upper = word.toUpperCase();
     return (
-      word.length >= 3 && word.length <= 8 && /^[A-Z]+$/.test(upper) // Only letters, no special chars
+      word.length >= MIN_WORD_LENGTH &&
+      word.length <= MAX_WORD_LENGTH &&
+      /^[A-Z]+$/.test(upper) // Only letters, no special chars
     );
   })
   .map((word: string) => word.toUpperCase());
 
-// Randomly select a subset for variety
-const WORDS = ALL_WORDS.sort(() => Math.random() - 0.5).slice(0, 500);
+// Randomly select a subset for variety using Fisher-Yates
+const WORDS = shuffleArray(ALL_WORDS).slice(0, WORD_POOL_SIZE);
 
 /**
  * Generate a random phrase from word combinations
diff --git a/main.ts b/main.ts
index c708fbd..4e5d093 100644
--- a/main.ts
+++ b/main.ts
@@ -1,4 +1,4 @@
-#!/usr/bin/env -S deno run --allow-read --allow-write --allow-env
+#!/usr/bin/env -S deno run --allow-read --allow-write
 
 import { Command } from "@cliffy/command";
 import { colors } from "@cliffy/ansi/colors";
@@ -104,17 +104,24 @@ class MorseGame {
       streak: session.bestStreak,
     };
 
-    await updateStats(gameResult);
+    try {
+      await updateStats(gameResult);
+    } catch (error) {
+      console.log(colors.red("\n⚠ Warning: Failed to save statistics"));
+      if (error instanceof Error) {
+        console.log(colors.gray(error.message));
+      }
+    }
 
     // Wait for user to continue
     console.log(colors.gray("\nPress Enter to continue..."));
     await new Promise((resolve) => {
       const buf = new Uint8Array(1);
       Deno.stdin.setRaw(true);
-      Deno.stdin.read(buf).then(() => {
-        Deno.stdin.setRaw(false);
-        resolve(undefined);
-      });
+      Deno.stdin.read(buf)
+        .then(() => resolve(undefined))
+        .catch(() => resolve(undefined))
+        .finally(() => Deno.stdin.setRaw(false));
     });
   }
 
@@ -130,10 +137,10 @@ class MorseGame {
     await new Promise((resolve) => {
       const buf = new Uint8Array(1);
       Deno.stdin.setRaw(true);
-      Deno.stdin.read(buf).then(() => {
-        Deno.stdin.setRaw(false);
-        resolve(undefined);
-      });
+      Deno.stdin.read(buf)
+        .then(() => resolve(undefined))
+        .catch(() => resolve(undefined))
+        .finally(() => Deno.stdin.setRaw(false));
     });
   }
 
@@ -148,10 +155,10 @@ class MorseGame {
     await new Promise((resolve) => {
       const buf = new Uint8Array(1);
       Deno.stdin.setRaw(true);
-      Deno.stdin.read(buf).then(() => {
-        Deno.stdin.setRaw(false);
-        resolve(undefined);
-      });
+      Deno.stdin.read(buf)
+        .then(() => resolve(undefined))
+        .catch(() => resolve(undefined))
+        .finally(() => Deno.stdin.setRaw(false));
     });
   }
 
@@ -171,8 +178,15 @@ class MorseGame {
     );
 
     if (confirmed) {
-      await resetStats();
-      console.log(colors.green("\n✓ Statistics have been reset.\n"));
+      try {
+        await resetStats();
+        console.log(colors.green("\n✓ Statistics have been reset.\n"));
+      } catch (error) {
+        console.log(colors.red("\n⚠ Error: Failed to reset statistics"));
+        if (error instanceof Error) {
+          console.log(colors.gray(error.message));
+        }
+      }
       await new Promise((resolve) => setTimeout(resolve, 1500));
     }
   }
@@ -224,7 +238,14 @@ class MorseGame {
       streak: session.bestStreak,
     };
 
-    await updateStats(gameResult);
+    try {
+      await updateStats(gameResult);
+    } catch (error) {
+      console.log(colors.red("\n⚠ Warning: Failed to save statistics"));
+      if (error instanceof Error) {
+        console.log(colors.gray(error.message));
+      }
+    }
   }
 
   /**
@@ -284,8 +305,15 @@ await new Command()
     );
 
     if (confirmed) {
-      await resetStats();
-      console.log(colors.green("\n✓ Statistics have been reset.\n"));
+      try {
+        await resetStats();
+        console.log(colors.green("\n✓ Statistics have been reset.\n"));
+      } catch (error) {
+        console.log(colors.red("\n⚠ Error: Failed to reset statistics"));
+        if (error instanceof Error) {
+          console.log(colors.gray(error.message));
+        }
+      }
     } else {
       console.log(colors.yellow("\nCancelled.\n"));
     }
diff --git a/morse.ts b/morse.ts
index 1cf88b3..e643af1 100644
--- a/morse.ts
+++ b/morse.ts
@@ -54,24 +54,51 @@ export const MORSE_TO_TEXT: Record<string, string> = Object.fromEntries(
   Object.entries(MORSE_CODE).map(([key, value]) => [value, key])
 );
 
+/**
+ * Check if a character is supported in Morse code
+ */
+export function isCharacterSupported(char: string): boolean {
+  return char.toUpperCase() in MORSE_CODE;
+}
+
+/**
+ * Validate if Morse code string is properly formatted
+ */
+export function isValidMorse(input: string): boolean {
+  // Valid morse contains only dots, dashes, spaces, and forward slashes
+  return /^[.\-\s/]*$/.test(input);
+}
+
 /**
  * Convert text to morse code
+ * Unsupported characters are silently skipped
  */
 export function textToMorse(text: string): string {
   return text
     .toUpperCase()
     .split('')
-    .map(char => MORSE_CODE[char] || char)
+    .map(char => MORSE_CODE[char])
+    .filter(code => code !== undefined)
     .join(' ');
 }
 
 /**
  * Convert morse code to text
+ * Invalid morse codes are replaced with '?'
  */
 export function morseToText(morse: string): string {
+  if (!isValidMorse(morse)) {
+    return "";
+  }
+
   return morse
     .split(' ')
-    .map(code => MORSE_TO_TEXT[code] || code)
+    .map(code => {
+      // Handle empty strings (multiple spaces)
+      if (code === '') return '';
+      // Return the decoded character or '?' for unknown codes
+      return MORSE_TO_TEXT[code] || '?';
+    })
     .join('');
 }
 
diff --git a/stats.ts b/stats.ts
index 3d32f32..1a4311c 100644
--- a/stats.ts
+++ b/stats.ts
@@ -98,11 +98,17 @@ export async function loadStats(): Promise<GameStats> {
  * Save stats to JSON file
  */
 export async function saveStats(stats: GameStats): Promise<void> {
-  const statsPath = getStatsPath();
-  const dataDir = join(Deno.cwd(), "data");
+  try {
+    const statsPath = getStatsPath();
+    const dataDir = join(Deno.cwd(), "data");
 
-  await ensureDir(dataDir);
-  await Deno.writeTextFile(statsPath, JSON.stringify(stats, null, 2));
+    await ensureDir(dataDir);
+    await Deno.writeTextFile(statsPath, JSON.stringify(stats, null, 2));
+  } catch (error) {
+    throw new Error(
+      `Failed to save statistics: ${error instanceof Error ? error.message : "Unknown error"}`
+    );
+  }
 }
 
 /**
diff --git a/ui.ts b/ui.ts
index d7f886e..f0d5eff 100644
--- a/ui.ts
+++ b/ui.ts
@@ -1,6 +1,13 @@
 // UI utilities and game interface
 
 import { colors } from "@cliffy/ansi/colors";
+
+// UI Constants
+const WAIT_TIMES = {
+  DEFAULT: 2000,      // 2 seconds for default modes
+  WORDS: 6000,        // 6 seconds for words mode
+  PHRASES: 8000,      // 8 seconds for phrases mode
+} as const;
 import { Confirm } from "@cliffy/prompt/confirm";
 import { Input } from "@cliffy/prompt/input";
 import { Select } from "@cliffy/prompt/select";
@@ -100,10 +107,10 @@ export async function showTranslator(): Promise<void> {
   await new Promise((resolve) => {
     const buf = new Uint8Array(1);
     Deno.stdin.setRaw(true);
-    Deno.stdin.read(buf).then(() => {
-      Deno.stdin.setRaw(false);
-      resolve(undefined);
-    });
+    Deno.stdin.read(buf)
+      .then(() => resolve(undefined))
+      .catch(() => resolve(undefined))
+      .finally(() => Deno.stdin.setRaw(false));
   });
 }
 
@@ -248,23 +255,35 @@ export async function playRound(
   );
   console.log(colors.dim("     Use / for word spaces\n"));
 
-  // Create a promise that rejects after the time limit
-  const timeoutPromise = new Promise<string>((_, reject) => {
-    setTimeout(() => {
-      reject(new Error("Time's up!"));
-    }, timeLimit * 1000);
-  });
-
   // Get user input with timeout
   let userInput = "";
+  let timeoutId: number | undefined;
+
   try {
+    // Create a promise that rejects after the time limit
+    const timeoutPromise = new Promise<string>((_, reject) => {
+      timeoutId = setTimeout(() => {
+        reject(new Error("Time's up!"));
+      }, timeLimit * 1000);
+    });
+
     const inputPromise = Input.prompt({
       message: "Your answer:",
       minLength: 0,
     });
 
     userInput = await Promise.race([inputPromise, timeoutPromise]);
+
+    // Clear timeout if input was received first
+    if (timeoutId !== undefined) {
+      clearTimeout(timeoutId);
+    }
   } catch (error) {
+    // Clear timeout on error
+    if (timeoutId !== undefined) {
+      clearTimeout(timeoutId);
+    }
+
     if (error instanceof Error && error.message === "Time's up!") {
       console.log(colors.red("\n⏰ Time's up!"));
       userInput = ""; // Empty input for timeout
@@ -299,11 +318,11 @@ export async function playRound(
   }
 
   // Longer wait time for words and phrases
-  let waitTime = 2000; // Default: 2 seconds
+  let waitTime: number = WAIT_TIMES.DEFAULT;
   if (session.config.mode === "words") {
-    waitTime = 6000; // 6 seconds for words
+    waitTime = WAIT_TIMES.WORDS;
   } else if (session.config.mode === "phrases") {
-    waitTime = 8000; // 8 seconds for phrases
+    waitTime = WAIT_TIMES.PHRASES;
   }
 
   // Wait for user to continue