The rule in my house is if your teeth touch my hand the game is over. Which means if we are playing/hanging out whatever and teeth so much as touch me I say "ouch" in a high picth voice, get up and walk away and my puppy is totally ignored for 5 minutes. Then I come back and play as if nothing has happened, if the teeth come out and touch me again, "ouch" and another 5 minutes of being ignored. If you (and everyone) are consistant, it won't take long for your puppy to learn.