Wait - are the horses going outside or not?
IMHO - If there is room in an 8 x 10 stall to kick manure to the side, there can't be much manure.
Sure there can. I used to board at a stable we're the stallions stall was never cleaned nor did he get out for excersize and it just mounded up in the corner. In 2 years I saw him out of the stall maybe twice except to breed a mare