We were at the Toronto East Regional yesterday and decided we also needed a tethered ramp. We decided to cut a grey tote and it worked out exceptionally well:
https://www.youtube.com/watch?v=Vdb_uN4r8_Q
That is in the practice field. In competition, if we lined up with the end of the ramp, we could sit still and feed an internal stacker our robot employs. We're stacking at the speed of the human feed station! Once we sorted out some robot issues, our day turned out pretty well.
We used a braided nylon line for our tether. So far, no issues with it getting caught in the wheels.
David