How to keep dogs from peeing on my mailbox post?

Put a fence around it. Then they'll pee on the fence....

Sounds like an impossible task! The only way to keep the dogs away from the post is to put some kind of border around it so they can't reach the post. Rocks, flowers, fence. But you will still have dogs visiting and marking.

Dogs usually sniff before they mark. You can spray the post with something unappealing to dogs. They have commercial stuff or you can try home remedies. Vinegar and water. Olive oil and lemon juice.

Or you could plant something thorny like rose bushes so that they cant get close. Some dogs don't like marigolds.

I agree it will be hard to stop but if it is possible.

Try Bitter Apple Spray. Needs to be reapplied after every rain event.

Bird tines around the bottom of the box. These are bird deterrents but they work great for dogs. Harmless solution. Go to Amazon and search bird be gone enviro spikes.