Back in the day when I worked in the wrecking yard we used to mark the end of the aisles with axles that we would pound in the ground and spray paint with fluorescent colors. When we finally closed the yard, we crushed all the cars that were left, pulled the axles out of the ground and sent everything to the scrap mill. The C body axles were a favorite for the task because we had so many of them and they never sold.