How to stop a puppy biting
To stop puppy biting, you should apply the same education to the pups that it would get in its pack. This means, you should combine a sound response with a physical response.
The typical sound response the puppy would get in its pack is a short, loud, high-pitched yowl - a sound that the pups will only ever hear in this exact situation, so it is a unique response to its nipping or biting.
The typical physical response is a short pinch in the ruff of its neck. This stretches the puppy's head upwards in reflex which provides feedback right through to its snout to open up the jaw.
How to stop puppy biting
This way, your response to the puppy's nipping or biting closes the circle - within a few times your pups will realize: If I bite, my ears will hurt from a loud, high-pitched yowl, I feel pain in my neck, this pulls my head upwards, which stretches my jaw and forces me to open my mouth. Using my jaw on someone doesn't do me any good.
This is a fundamental part of nature's puppy training whilst still among the litter, and you should replicate it in your German Shepherd puppy training too. This is how to stop puppy biting. When you subscribe to the MYGERMANSHEPHERD PERIODICAL, over time you will find out more interesting ways how to stop a puppy biting.
Now, because you have the advantage of being a human and not part of the litter, you should use this opportunity and combine it with the first basic example of obedience commands as part of your German Shepherd obedience training: Say a sharp, short "No!" after the yowl while you are pinching the pup's neck. This way, within a few times your pups will learn to stop doing something when you say "No!" - not just to stop puppy biting.
If you still have a GSD puppy, this is a great time for you to learn to read the German Shepherd body language - a regular topic of the MYGERMANSHEPHERD PERIODICAL. Although your dog's expression of feelings via its body movements will naturally become more accented when your German Shepherd puppy grows up, a GSD puppy develops its own characteristic German Shepherd body language at the time it is about eight to ten weeks old.
Dog owners who have problems with their dogs, in fact have a problem to understand their dog’s body language. While we humans make a lot of use of our voice to express our feelings, dogs express almost every feeling and mood through their dog body movements - even more so if you forbid your GSD to bark, see German Shepherd barking.
Also consider this: Unless you are able to read the German Shepherd body language you cannot know if your German Shepherd puppy training, or later your German Shepherd dog training, was successful to stop puppy biting or future dog biting. You would only know that your training efforts were definitely unsuccessful the moment your puppy bites or your adult dog bites. To be sure and safe all the time, you must understand your dog's body language.
If you still have children in the house too, this is even more important. Motivate them to consciously observe your German Shepherd as well. Use specific situations to read the German Shepherd body language and to explain to your children what your GSD is likely to feel at the moment, hence what his movements mean. This will not only make your children much safer in dealing with the dog when they are taking it for a walk, but it should also help them to notice and interprete the human body language and the adult world around them when they grow up.