That's a good idea, but what happens when a bunch of cars are sitting in front of the cones & you can't see them? I've tried about 10 different ways of marking them, but it doesn't look good to a visitor or me. When you have 60 cars in a yard & the magnets are about 3 ft. apart the cars hide everything. There's got to be a cheap way of doing it w/out electronics, but, I haven't thought of it yet. I had put in long wood stir sticks & painted them flat black & put a spot of brite red paint on top, but everytime I reached across the area I snapped them off at the base. Just thought of something that might work even better. How about a small stick on a coil spring base attached to the table top W/a small red bead glued to the stick? Funny, what pops into the old mind(mine).