You have three choices with any conflict with your ex: (1) Just let it go; (2) Try to calmly reach a resolution that deals with both sides' concerns; (3) Sue for enforcement.
By the time you make a post asking for help, you've decided that option 1 won't work for you or your children. Option 2 is really hard for most people--they got divorced for a reason and that reason often involves an uncanny ability to push each other's buttons. That leaves option 3.
If you sue for enforcement, you'll need an experienced family law attorney. An experienced attorney might be able to do some Option 2 work once the suit is filed and he or she has your ex's attention. And if you consult with an experienced family law attorney who will be able to ask you detailed questions about all the facts in your case and examine your final decree carefully, the attorney may find other leverage in there.
It sounds like Mr. Daley has laid out the options well, and he's right...you probably are to the point of beginning an enforcement action. And it is definitely a pick your battles measure. His conduct will almost certainly continue unless you do stop/slow it by an enforcement action.
You know your ex better than any attorney will, so you should also think about the long-term implications. Specifically, can an enforcement now also help you avoid some of his senseless actions like this in the future. Oftentimes it will, and that may be an added bonus for you here.
I agree with Mr. Daley, speak with a veteran family attorney and know your options.