You're right that fines are no deterrent, but inconvenience is. I don't know the legality, but if landowners/police could put a Denver Boot on cars illegally parked, drivers would learn their lesson really quickly should it take them an hour to call someone to remove the boot and they were late for supper or coffee with their friends.

At CNA-Q, they tried parking arms but the steel camels just crash through them. So they went back to the old system: if you park illegally, you get a sign taped to your windshield that basically says, "If you park here again, I'm going to tell my boss!" Doesn't get much stronger than that!