Hi. My chicken run will be on a large concrete area and its getting very difficult to decide what would be the best substrate. Pebbles don't absorb the poop so can be washed however there's a chance the poop will collate underneath without excellent drainage. Wood chip with probably get poo stuck and scratched all over it, unusure how often is needed to replace and then sand will likely get wet and compacted with poop and smell badly. Im actually starting to put myself off my chicken project due to the simple problem of how ill keep them clean. I could try straw but I'd need bales of it to cover 17x10 ft run and with the rain and poop may not last long. Anyone got any ideas?