So far- I think ..
*Resin w/ hardener
*Cut all wires in engine bay
*take out oil of engine and ******..but drain them into a pan so you wont leave a mess so he wont know.
*pull his driveshaft (easy to do on most cars) and he wont know wtf to do
*take valve stems in tires and put screws in it
*If possible, take out all of his headlights and bulbs, and brake lights
*Take a diamond-cutter and scratch all of his windows to the point where you can barely see anything out of them
*Wipe shit all over the car, as a final "**** you"
Or you could take a stungun to his antenna, and it will immediately fry all circutry in his car. All electronics will be fried....this would be an idea you would seriously want to consider, because of its effectiveness and expensive cost to fix.