You need to get in touch with his commanding officer. He is not allowed to do this. The military will make him hand over the info, literally. The child support should come directly from his pay check, and should change when his rank changes, automatically.
If you ever see him in uniform... it's not hard to tell what rank he is.
Take him back to court if you have to, they will mop the floor with him. The military will not allow him to act like this, believe it or not they do have codes and standards of conduct. Get the military involved. There are many places and organizations that can help you do this.
His behavior may even lead to a loss in rank.