The next time your dog bites scream "OW" in a high pitched voice. Exaggerate a little. Then refuse to play with him, turn your back to him and don’t pay attention to him for a few minutes. If he doesn’t get the message scold him in a low-toned, threatening voice. Exaggerate that too. Sound meaner that you really are. Don’t touch him.

Have a shake can and use in conjunction with a firm "no bite." Praise as soon as he stops biting or mouthing. Timing is critical, and you must be consistent.

Push your hand further into his mouth (do not do this with an aggressive dog) this will cause your puppy to try and "spit out" your hand. When he does praise and reward him with a toy. Say "no bite". Praise when he stops biting or mouthing.

For the dog that is biting the leash, chances are you played tug of war with your dog when he was a pup; what’s cute as a puppy is sometimes obnoxious as an adult. First of all, stop all tug of war. Dogs cannot understand any rule that has exceptions. If he can play tug of war with a toy, he thinks he can play it with the leash. As your dog starts biting the leash give your dog a corrective jerk and at the same time say "no bite". Make sure you praise him immediately when he stops biting. If your dog is very persistent you can try spraying the leash with bitter apple.

Pick one method and give it a fair try. Don’t skip from one method to another as this is confusing to the dog. Don’t give up after one or two attempts. It took your dog some time to learn this behavior and it will take time to learn not to bite.