Years back, some young punks were using M-80s and other heavy-duty firecrackers to destroy mailboxes. After three of his were blown up, one old farmer got tired of it. He built a post out of two 8-inch I-beams, covered it with concrete and rebar, mounted a standard mailbox on a 2 inch thick steel plate, wrapped the entire mailbox and plate with 3/4 inch copper cable, poured four more inches of reinforced concrete around all of it, and set granite stones into to give it a sort of rustic exterior.

Two nights later, the punks did the M-80 trick and mailbox remained intact. Several tries later they shoved two sticks of dynamite into the mailbox -- and blew the door off. They then gave up.

True story -- I was NOT among those involved, but I someone who was and he told me the story and I have no reason to doubt it. The farmer, by the way, was my great-uncle.