I'd have to put up a sign notifying cars will be towed. I simply don't want to have to deal with the problem. Why should I have to deal with this in a residential neighbourhood where my expectation is to have an actual neighbour who understands his property line?

Putting the onus on me to deal with his guests is a problem that bothers me in of itself.

If you had the same situation I am sure you'd grow tired of it pretty quick.