Alright, basically my current idea would be to do something totally random and fair...like say i pick a number from 1 - 100 or something. Then someone just has to guess the number...the key is, if one user makes two guesses within a 24 hour span, they get kicked out of the competition. That way people just won't spam it. I dunno, maybe that would be stupid.
I just wanted to ask first cause I didn't know if just giving away pin numbers would be cool with you guys.