What happens if a trained protection dog bites for no reason?

Answer 1

That's a liability nightmare. Because the dog was intentionally taught to bite, even if only for sport or protection, vicious dog law generally hold the owner to a higher standard on containing his dog. Training-wise, it's a serious problem that requires expert help from a trainer experienced in protection training. This is not a fix-it-yourself project.

Answer 2

The offended dog bites the offending dog back for a good reason.