"My puppy is biting me and ripping my clothes! How do I get him to stop?!"

By nature, dogs use their mouths for play, communication, defense, and manipulation of their environment. Puppies need to learn what is an acceptable surface for mouthing and acceptable pressure to apply with their jaws. Dog-playmates can help teach them this but the job falls mostly to the human handlers. Here's a way to teach this without having to spank, yell, bite back (!), pinch ears, or nose whack your dog:

Get lots of toys so you can always carry one or have it within reach for him to mouth. They don't have to be expensive toys, just tie knots in sturdy pieces of cloth like an old pair of jeans and trim the ends off. Don't let him lie down and chew on these, they are only for play, he should chew on raw beef bones, rawhides, or Kong-type toys. When he approaches you looking for trouble (you know that look!) make sure his mouth meets the tug. Try to anticipate when he's going to be a brat and invite him to play BEFORE he starts poking at you, don't let him be the one who decides when play starts and stops. 

If he transfers from the toy to your shirt or hands while you're playing, yelp loudly, turn away and "be a tree". Ignore him until he quits jumping or nipping at your legs, keeping the toy out of reach. Tucking your hands into your armpits may help. It may feel like the dog is owning you as he pokes, barks, jumps or nips. It may even be painful. Just practice your aloof sneer and wait him out, or climb somewhere he can't reach. Remember, you're bigger and smarter than him and you have the toy. Once the excitement level in the space has dropped considerably with your cold-shoulder treatment, you can re-engage the puppy in play.

Some people recommend tapping the dog on the nose when it nips you. For some sensitive dogs, that is enough to make them wary about playing with you-- this is how submissive urinaters are made. It's not a good idea to physically punish a soft dog, a loud "no", feint, or walk away is usually plenty. For average or hard dogs, a tap on the nose is like poking a rowdy 7-y-o boy in the shoulder. You will train a dog to push through punishment to get what it wants if you give minor and ineffective whacks that don't really deter the dog. If you want to use punishment to influence a dog not to put his mouth on you next time, you would have to hit him hard enough to make him squeal and cower. Most people don't want to punish that hard, nor is it necessary. Use the "stop play" punishment described and continue to teach the dog that fun happens when his mouth is on the intermediary toy, not your clothes or skin.

Train an "out" command. Use a fairly rigid tug toy, not a rag, rope or stuffed animal. Get into a good game of tug with your dog, then say "out" or "drop it" and immediately freeze the toy. It works best to brace it against your knees or thigh. The dog will look at you puzzled and continue tugging for a while. The moment he loosens up, if only halfway for a rebite, mark ("yes!") and start playing again for about 10 seconds. Repeat. Up the criteria to the dog must completely remove his mouth before the game starts again, but always resume promptly, don't make the dog wait more than 2 seconds, that's plenty of time for you to tell him to sit, bite, or take a break. Don't play tug with a teething puppy!

Train an "all done" signal and be consistent about moving away and ignoring the dog after you've given it. Moving in a large circle around the yard or room after the "all done" signal will encourage him to cool down and switch his focus to the direction he's traveling rather than staying centered on you.

Light "biting" (mouthing) and air-snapping is "normal" for dogs of any age because they use their mouths for social play, communication, defense of resources, and manipulation of their environment. However by 1 year of age, most dogs who live alongside humans have been taught to keep their mouths off of people and cope with the stresses in their environment. A few older dogs will still mouth fairly hard in play just because they were not taught otherwise during puppy-teething stage but if the dog actually punctures the skin, that is more than an annoyance, it is a public health hazard. This article may help you: http://www.kerryblues.org/WDJ/BITTEN.HTML