ok, this idea is way out there but here goes. I don't have a rock tumbler but was thinking, what if I took some clad and a handful of sand and put it in a small gatorade bottle, then wired the gatorade bottle to one of the wheel covers on the car. Then drive the car on the mail route, or checking cattle on the farm, or teaching the teenager how to drive in the school parking lot. You wouldn't want to get out in traffic and go high speeds though cause it could cause the bottle to come off.