We will be using panels to line our riding arena and will put maybe 2' to 3' used conveyor belting on the bottom of the panels to hold the arena footing material in there.
Low enough to see over it when sitting on the side lines, high enough to keep pesky dogs from running in there.
At the base of gates, it will brush along as you open and close them.
There are other web sites with those materials, but that one had neat pictures of what all is out there and some of the possible uses, some for footing base for muddy areas around barns also.
Luckily that recycle yard is here in Denver. I am going there Wednesday for some snow tire base pans, for feeding hay out in the arena. The yard is relatively near the Natl Western show complex, if you ever go to horse shows there.
They have an email list you can get on for when new stuff becomes available.