This is a huge problem.

A while back there was a discussion of police officers who were fired/convinced to leave for abusive conduct who promptly became officers in other towns becasue the terms of dismissal or fear of lawsuits prevented their misdeeds from being shared with the other forces.

On the other side there is the valid concern that a vicious or vindictive boss may unfairly poison the well for someone who leaves (even legitimately) under controversial circumstances.