It'll eventually rot, but it's easy to replace it again when it does. If you have a problem in your area with vandalism, sink a good steel post in concrete. Our neighbor did that after having some kids destroy his mailbox repeatedly. He replaced the box with a thick steel one, so the kids (meaning teenagers) couldn't dent it. They decided to pull it out of the ground with a chain instead. The box only tilted it a tiny bit, but they left their car bumper near the post, still attached to the chain when they left.