see:
Bite Inhibition how to teach it
"1. No painful bites. 90% of puppies will stop if you give a high-pitched squeal or yelp. If they stop, praise and reinforce by continuing the game. The other 10% and puppies who are tired or overstimulated will escalate their behavior instead of stopping. This requires you to confine the puppy or end the game. Remove all attention. It does *not* require any added aversive -- yelling, popping the nose or under the chin, shoving your hand down his throat, or spraying with water.
If you end the game, you need to be able to get away from the puppy with as little fuss or attention as possible. Even negative attention is attention. It's often helpful to have the puppy tethered, so you can simply move back out of his reach. Or, have him in a confined area and simply stand up and move past a boundary. Because the getting up and moving is tough to do at the instant the undesired behavior occurs, consider using a hand signal that will always mean "You're a jerk. Fun's over." Use it consistently when poor behavior occurs and you're going to withdraw attention.
I am well aware that puppy teeth hurt, and that this step can be overwhelming. Do it when you can, and at other times redirect, redirect, redirect. Puppy mouthing is a 100% natural dog behavior. It's not dominant. It's not meanness. It's a puppy being a puppy. When it's too much either redirect or end the game. Aversives are confusing, unfair, and unnecessary."
On reason the dog bite harder, more aggressivily is it succesfull in gaining your attention. some things to think about from
Simple Solutions to Dog Behavior Problems
"~ Dogs are like children when it comes to the need for attention. They would rather be praised than punished. And they’d rather be punished than ignored. Catch your dog in the act of doing something RIGHT, like chewing on his bone instead of your shoe, and praise him for the GOOD behavior
~ Think REDIRECTION before correction. If you catch your dog in the act of misbehaving, REDIRECT the negative behavior to a positive alternative. When you find your dog chewing on your slippers, take him to his toy box and play with one of his toys with him for a few minutes. If your dog is digging in the yard, stop and play a quick game of Frisbee to tire him out.
In summary, consistency is the key to owning a well-mannered dog. It’s not fair to your dog if you occasionally allow misbehavior (such as begging at the dinner table or lying on the couch). Your dog will become very confused at your unpredictability"