Basically, get a police report for every START of visitation PERIOD (not every single day unless you want to be chewed on). File them as they come. Don't file for actual Contempt until you have at least a couple. Gather affidavits/declarations from witness' etc.
Then, they are admonished/reprimanded by the court....or fined...anything up to losing Custody. But you have to follow procedure. Start with documenation, then demonstrate history, then move on to Enforcing the Orders, then Parental Interference, etc. etc.