My suggestion would be to NOT go out with your guns blazing on this.... even if he has problems, you will have a VERY difficult time actually proving that he is doing things that will supersede his rights. The court will be VERY neutral on value judgments, and you could in fact hurt your own case. Just be above board, wait for bad things to happen, document them, and then use that information after the fact. My sister had a nasty divorce with her ex, he's really a moron, got a drunk driving, lost his job etc... none of these things made a difference in his parental rights. So go after your own custody, focus on yourself, and avoid disparaging him in front of the court unless you have a conviction or total proof that he is not capable.