my dad got pissed that our mail box was getting hit by plows, baseball bats, and shotgun fire (yeah, shooting mailboxes is like a hobby around here). SO, as the owner of 2 steel fabrication companies he had a 12 foot piece of 1/2" thick 4x4 pipe put in concrete. on top of the pipe he had a 3/8" steel plate mail box welded on.
that winter the drunken driver of a ford f250 hit it at 30 mph head on which put a complete V in the front of the truck. besides paint damage, the mailbox was unharmed... later that year it was shot with a shotgun which barely chipped the paint, then shot with a slug that dented it a whopping 1/16th of an inch. havent had any problems for 4 years since!