EweSheep, where do you get horse rubber mats! how long have you used them? how big are they?
Any farm store would have them. I get mine from Menard's, which it was really a people rubber mat which has lasted me over seven years and still going strong before the mice gnawed holes in it from the bottom (my fault, for not putting hardware wire on bottom so that the mice don't gnaw the wood subflooring). I just recently replaced it with truck bed rubber mat last year and it looked just as good as my original rubber mats. No glue downs, just lay them down. I took a shovel to it a few times and it didn't even faze it. I had washed rubber mats as well and it cleaned out GOOD! (I have a resin shed which the metal tack down lays on top of the rubber mat so I don't have to worry about rot. Be sure to overlap a few inches past your wood foundation so it will drain the water out of it. Or if you have a regular shed, no washings needed, just a stiff brush to remove caked down manure (like you do for horse stalls).