Australian Shepherds, like all dogs, nip and bite for a variety of reasons. To train your Australian Shepherd to stop nipping and biting, you should first identify the cause of the behavior. Common reasons for nipping and biting include:

1. Teething: Puppies go through a teething phase where they will chew on anything they can find to relieve the discomfort of new teeth coming in.
2. Lack of socialization: Dogs that are not properly socialized may be more prone to nipping and biting out of fear or uncertainty.
3. Playfulness: Some dogs will nip and bite during play as a way to initiate or maintain play.
4. Lack of training: Dogs that have not been properly trained may not understand what is and is not appropriate behavior.

Once you have identified the cause, you can work on addressing it through training and behavior modification techniques. These may include:

1. Providing appropriate chew toys for teething puppies
2. Socializing your dog with other people and animals
3. Teaching your dog appropriate play behaviors
4. Teaching your dog basic obedience commands such as “no bite” or “stop”
5. Consistently rewarding good behavior and ignoring or redirecting bad behavior.

Consulting a professional dog trainer or behaviorist may be helpful in finding the right approach to your specific dog.