Driving cars up ramps on slippery surfaces

I cant take credit for this one, but I do have an improvement. do your ramps "skate" accross the smooth garage floor as you try to drive up them? Same thing in gravel? An old tie down or seat belt strapped to the top of the ramps and placed under both wheels on the same side of the ramp will stop it from sliding away. For better results, my improvement is to fasten the strap around the drive wheel so it is essentially a pully making sure the ramp goes under the wheel.
*****disclaimer Note that ramps are really dangerous, make sure there are other people around, underneeth, infront, behind, or anywhere else. be careful, its easy to launch off ramps or put them all the way underneeth the car.