that the coach follows the rules. These types always have a hard time following the rules. Check their bats, track their boys playing time, track pitch counts and days of rest, when the guy realizes what you are doing and complains about it. You just let him know that you suspect him of cheating.

Also remember that half the boys on that guys team hate being on that team. Make sure that when they play your team they get their field time and at bats.