My father had a friend who worked for one of the local County transportation departments, and my father's best friend would get into his old car (which, as my father described it, was almost an M4 Sherman tank) and go looking for the road crews' barrels out in the boonies, many years ago. Well, the best friend would mow them down. Said other friend got pissed off, and one day filled one of those barrels with all sorts of rip rap and BFRs (Big ****ing Rocks). So, the best friend was out with the gang that oncoming weekend, mowing down barrels, and WHAM! They found the one that had 400 lbs. of rocks in it. For some strange reason, said best friend never did that again . . .
My brother told me a story from a friend of his that had trouble with his mailbox getting hit and run over about every other week. Friend finally got tired of it and sank a 6X6 I-beam about 4 feet into the ground, boxed it up to look like a 6X6 post, and put his mailbox on top of it.
Two weeks later, he came out one morning to a car "parked" on top of the mailbox post. No more problems after that.
We used to have problems every now and then with kids coming down my road and hitting mailboxes with bats or whatever. A few of us fabricated some mailboxes out of 1/4 inch plate steel (a guy down the road had a machine shop and rolled the plate for us), painted them to look just like a new box, and welded them on top of 4 inch pieces of steam conduit. In the 10 years since we've done that (some of those boxes are still standing), no mailboxes have been damaged, although one of the "good" ones has a few dings.
The BEST mailbox I've ever seen is on one of the routes I sub on. It's made out of 1/2 inch thick 4X10 rectangular tubing stock, with 1/4 plate welded on one end, and a door made out of 1/4 plate and 1X1 angle iron. I bet the thing weighs 200 pounds, because the door weighs 10! (And YES, I said 1/2 inch thick. It's bulletproof, literally.)
Makes my hands sting just thinking what hitting it with a baseball bat would feel like.