When I was a kid, my neighbor Mr. Benson, was apparently on the receiving end of a bit of mailbox mischief. At some point, he got fed up. He made himself a new mailbox out of pipe, crafted a door, made a neat little platform for the mail to sit on and mounted the whole affair onto an I-beam, probably set several feet into the ground in a hefty pad of concrete. As far as I know, his new mailbox was never touched again. Fast forward a bit, and the kids of the old neighborhood now have mailboxes of their own to protect.
When he made his mail fortress, it was brightly painted in blue and yellow, a nice stainless knob still gives the user an easy way to open on the custom hinge. Decades later, his Vandal-B-Gone mailbox still stands, though it needs a bit of sand blasting and paint.
On a bike ride from my aunt’s house the other day, I saw several examples of similar constructions designed to thwart the casual ne’er-do-well hanging out the passenger side window of a night time batting practice run. But these were nothing like Mr. Benson’s bombproof box.