Shock treatment... will slow 'em down anyway. I once met a cruising couple that had a homemade electrically charged system aboard, he was a merchant seaman and would leave the boat for weeks at a time leaving his wife aboard by herself in some dicey places. She would charge it up and turn it on at night when she was alone. She said it stopped a bad situation from getting worse a couple of times, they had other "systems" in place as well for dealing with the unwanted.