Idea: Replace CAPTCHAs with simple homophone questions.
Your/You're fired!
Type in the correct word.
Their/There/They're all gonna laugh at you!
Type in the correct word.
They would be practical grammar flash cards.
Idea: Soccer clubs customize their home fields with sand traps and varied grass heights to spice up play.
Query / # Google Hits
"your fired" / 404,000
"you're fired" / 3,280,000
"their all gonna laugh at you" / 10,900
"there all gonna laugh at you" / 37,100
"they're all gonna laugh at you" / 303,000
You're fired!
They're all gonna laugh at you