Many professional trainers believe that hard mouth can be a hereditary affliction. When selecting a puppy, by all means check out the parents first. Still, there is really no surefire way to tell if a dog is going to be predisposed to damaging birds once it grows up. That part likely falls in the luck-of-the-draw department. There are, however, precautions you can take while training your retriever puppy that may help prevent the dog from developing hard mouth. Common sense applies in most cases.