How are you going to stop a dog from peeing on the mailbox post? Don't think so, especially if it is a dog just running around the neighborhood, which is not supposed to happen around here because of the leash laws, but does happen all the time.
If I was walking my dog, I would not let her pee on a mailbox post, but our street is really the only one in this area that has mailboxes out by the street, and there are only 4 houses on this street. The rest of the streets around have have the mailboxes on the side of the house.
Actually I never thought about this before, so if we had been walking along and she started to pee on a mailbox post I might not have worried about it because I figured it was somewhere a lot of other dogs had peed, so what's the difference. It's not like they could pee on the mailbox itself.