[cooke]

You might go get you a new "welcome" door-mat that is made out of thin carpet or astro turf. Then get you a piece of 1/2" plywood that is exactly the same size as the mat. Carefully drive a 100 or more 2 1/2" long "un-galavanized" nails through the plywood. Place the "welcome" mat on top of the plywood and slide it out far enough out that he'll need to step on it to reach the door-bell button or entice him with a pretty, new flower arrangement-wreath mounted securely on the door. Be sure to put a "no-trespassing" sign at the end of your sidewalk.
Usually this level of pain will cause him to think twice about retalliation.
We had a 'window" peeper at some apartments years ago that would jump the 6' high wooden fences that surrounded the sliding-glass doors and patio area. He would land quietly and then enjoy the next few moments staring into people's living rooms. He always did this very late at night. With a 4 X 8 sheet of plywood and several hundred rusty old nails and some old carpet; we decided it was pay-back time. It was especially satisfying to hear we had "nailed" him at 2:30 in the morning.
Usually it takes this kind of action to get your point across to people that your family is sacred and should not be tampered with. While to some this may sound a little extreme; they need to remember that this is your daughter he's chosen to single out. So there will be very extreme consequences for him to deal with.
BTW, I'm very sorry to hear about your divorce.