Neighbors driving through yard - solutions?

[Shawn Q.]

I have neighbors at one of my rentals driving through my back yard to get to the street (basically they have a shared driveway and the person at the back of their driveway drives through my back yard to get to my driveway on the other side of my house to get to the street). I'm wondering if anyone has dealt with this and has a good solution. Much as I hate the idea of the expense (it's a low-$ rental and the replacement time would be considerable) I'm strongly considering fencing the back yard. Also thought about laying down railroad ties on the property line, but those could be moved. In any case fence will likely need to wait for spring, so also looking for temporary solutions to get through to then if nothing cheaper than a fence is possible. 

[Dave Poeppelmeier]

You could drive the railroad ties into the ground with pieces of rebar (if the ground isn't frozen too solid). You have to slap them while saying they aren't going anywhere when you're done, Dad Rule.