Sounds like one of the other boxes on my route - Take one of those "2
foot wide by 2 foot tall by 3 foot deep" ultra-jumbo rural mailboxes
(You must know the ones I'm talking about - Practically big enough to
count as luxury accommodations for 3 families of cambodian refugees),
another "more standard for in town" style boxes of roughly the same size
and proportions, and half a bag or so of concrete - Mix well, center the
small one in the large one, and pour the void full of 'crete, then mount
the whole mess on a chunk of what looks to be 4 inch well-casing sunk
Idunno-how-deep in concrete.
Looks like it's been fairly effective - The mailboxes before and after
it have been nailed twice each (and look like they take frequent "minor"
hits besides) since I got the route, while the "concrete-lined" one has
a couple of minor dings, and has often been seen with the splintered
remains of broomsticks and ball bats nearby 
--
Oopps, ignore my last post.