Cover the valve stem caps with Crazy Glue or other strong adhesive just before you leave the vehicle. Then, when you come back, the culprit will be glued to the tire.
Or, put some gooey substance on the covers that is difficult to get off skin (tar, perhaps.) After one air removal episode, the culprit won’t do it again.
Lastly, you could put some corrosive material on the caps that will burn the culprit - but I do not recommend or condone doing this.