[KappaKittyCat]

When he does that, yelp. I'm serious. Mother dogs yelp when their pups nip, and the pups stop.

Secondly, keep in mind that dogs communicate just about everything using their mouths. When dogs greet each other, they do it by biting each other (not hard). Your puppy doesn't know any better. My guess is that he nips when he gets riled up due to overstimulation from some heavy play, so when he starts to nip, STOP PLAYING. Yelp, hold his mouth shut, tell him NO, and crate him for a while so that he can calm down.

Hope this helps.