One thing in this thread that was not mentioned is that he might want to consider keeping a journal of all events and things he does. Be sure he keeps his own emotions out of the journal, and only documents the actual events. This would be the phone call from the ex to pick up the kids, or the...
One item is to keep a journal of events. This journal should consist of the dates and things you do with and for your child, in addition to anything the mother says or does. This journal should also keep a record of all visits you make with or on behalf of your child to teachers, counselors...