i have a temporary run that has small flat smooth 3/4" to 1" pebbles that are approx 1/4" tall. (they were already in the area I put the run). Should I just use this or put down shavings or sand or???? I am worried that being that size might prevent the chickens from scratching them around and that the poo will just sit on top I am in Portland where it rains a lot. There is a gentle slope so should have some run off.