They sell "L" brackets you can install on the
doors. Depending on the neighborhood, that might be enough to discourage them, but a real ****head will just break the
door.
When I had some washes in bad areas, the best compromise I found was a piece of coathanger wire. I would cut off about a 6"piece, put it through the hole, double it over, and twist it together witha pair if lineman's pliers. It would keep the casual curious person out, but if they really wanted in they could get in without damaging the
door.
Frequent cleanout helps discourage it too, but a desperate addict looking for some change will still get in