I'm building my first chicken coop and trying to figure out what to use in the run. I've heard that sand is the best choice, but the gravel company we use only sells mason sand and I've read that that's too fine. They also have 1/8-3/8" pea gravel, 1/4-3/4 river rock, and 3/4-1.5 river rock. We're planning on buying half a yard and all of them are within $2 of each other, so price and quantity isn't a problem. We have a 4'x10' run that's mostly sitting on concrete (there's about 14" of dirt in the middle). My boyfriend wants to tamp gravel on top of the concrete and put sand on top of that. I know, I know, you shouldn't put gravel under sand! But, he figures that if he tamps it the sand won't wash out when it rains. I don't know if that's actually true, but oh well. So, would any of the gravels work? Or should I find somewhere else to get a heavier sand?