I currently just use my backyard, part of it is dirt. I have some structure laid down and laid a pallet over it to create a ramp. I had a couple large boxes to help but the latest rain sort of wiped it out. PLus I think the dogs like to chew on the cardboard. Otherwise I have a large rock...
I built a quick set up in the backyard since I had stuff laying around and its partly dirt anyways. I can always toss out the stuff and re purpose part of it if I need to. I might look into a plastic ramp or shoot even a cardboard box ramp that I have come across on Youtube... But parks have...