I used to drive a dually truck and often got rocks stuck inbetween the tires when going down logging roads out west. I was just watching a series of "IRT (Ice Road Truckers) and they had a neat trick. Instead of hitting the rock out, or prying it out with a crowbar and risking puncturing the tire, or hitting it with a hammer (my favorite), they tie a rope around the rock several times and then tie the rope to the bumper or a frame. Then they drive forward slowly. The rope (or chain if you had one) pulls the rock out. It was a pretty neat trick so I thought I'd share it here for anyone driving a dual tire trailer or truck.