How do those large rock/solid mailbox lawsuits usually work out? I thought that the owner can be liable because they left a "trap for the unwary" or some such. I'd like to install a few rocks or something, every one of my neighbors' trees has been hit at least once. The people two doors down had a loser drive through their bedroom at 6AM.
The person who built it wins, as seen by the various quotes here and elsewhere. Ever see big poles/potted plants sitting around buildings? They're there for the same purpose. One good spot to look would be around gas station pumps. Steel pipe, filled with concrete. It's not a trap, it's a defensive structure, especially if you've had somebody plow into your house before. There was a business that put three of them in after having their building smacked a number of times. With a house, it's merely been dressed up. Kinda like how most businesses use planters for their big blocks.
There's nothing in the law saying you have to have a break-away mailbox.
A rock, on your property, even a mailbox, on your property, is not a normal movement path for vehicle traffic. Matter of fact, you might be able to sue the drunk who smacks into your rock (preventing him from hitting your house), for damaging your rock!
You'd be in trouble if you dumped it on the road. But unless the idiot has an easement through your property, he isn't supposed to be driving there, and it's his responsability to keep his car under control and off your property.