I had the same problem as my garage floor is highly polished and even the rubber grip grips on the bottom of the ramps don't help. I drilled in a couple threaded expansion anchors into the concrete and just bolt a 1 ft long 2 by 4 to the floor in front of each ramp when i use them. This stops them from sliding. I keep them stored under a workbench when not in use and just leave the bolt attached to them.