Whats cute in an eight week old puppy, isn't cute when he weighes l00 pounds. You need to let him know NOW that nipping isn't appropriate behavior. Take his muzzle firmly in your hands and tell him shaprly "no". I have actually pinched the lips and said "no". The puppy has to learn who the boss is. Good luck. Puppies are like kids. They need to be taught what is appropriate behavior.