Here is the problem: The top hinge keeps rotating allowing the gate to fall off the hinge.

The 16' gate is hung on a 6" round fence post. The hinge is threaded and goes all the way through the post. I have a washer and bolt near the hinge, and a washer and bolt where the threaded portion comes out of the post. I tighten these bolts to the point the washers are sinking into both sides of the post. For some reason the hinge is still able to rotate with time and movement.

How do I stop the hinge from rotating and allowing the gate to fall off the hinge?

Hope that makes sense,

Thanks,

Joe