Here's how to stop the bowstring from hitting your arm
 

I made a video explaining how to stop it

http://www.youtube.com/watch?v=-yYev-3is54

you have too long of a draw or are not holding it properly...plain and simple...

Hold the bow correctly and you wont ever have the problem. Just saying

Couldn't agree more. If you're unable to correct the problem, an armguard is the ticket.

Ive only hit my arm once and it was because the draw was too long...Ive since corrected that and haven't hit my arm since...

have you tried the trufire 360 release?

Correct draw length is the key. Learning to cock that elbow just a bit is strange and awkward but after a bow shop guy instructed me to do that my shooting became more consistent and have never struck my arm with the string again. It becomes a steady pressure that you can actually feel when your form is perfect.

Don't straighten your arm let be loose but not to loose

This. A death grip on the bow is not good for accuracy due to torqueing the bow, but form and proper draw length will eliminate wrist slap.