@Wild Hair I haven't used the rubber mats, and I only have 11 but I had someone pour cement down and we built a pen approx. 20x17 ! And it has quite a bit of space for them. They even lay in the nest! But for me even with cement and it being winter we have a hard time scraping the poop off unless we really scrub down. Thinking of investing in a power washer. But back to subject, with duck poop, unless you get it while it's still wet it will get into the foam padding and with their little claws it will probably end up having to replace more often than you'd think. We wash our pen down every other day, once in a while two days in a row and it still seems to be a pain.... I don't know if the foam will hold up since their poop seems to stain the cement. I think it's eating the cement slowly, but I'm no expert.