how legal is a waiver

Your husband's situation is difficult, because employment in law enforcement is a very sensitive subject where quite a few of the ordinary rules don't apply.  And it is hard to give you any definite information, without knowing more about what led to his original layoff.  If he wants a more definite review of his rights, he should talk to an attorney in your area who is experienced in public employment law.  One place to look for a qualified lawyer is our website, http://attorneypages.com

Sometimes, in law enforcement, just the suspicion of wrongdoing can end a person's career. Even in ordinary civilian employment, most states' law gives you no recourse against a former employer who gives an unfavorable recommendation, as long as what is said is not knowingly and wilfully false.