How can I make my dog stop biting?

My dog is very well trained, he can do most trick easily and he is very friendly. His bites don't hurt, they are meant to be playful but it gets very annoying and when he is hyper he bites hard and even makes me bleed but I know he is playing. I always squeeze his mouth shut when he bites but he just gets mad and keeps biting. He is a male cairn terrier and almost a year old and I'm pretty sure he is done teathing.