I am moving my 5 chickens from their current coop and run which is about 3'x7' and only 4' high to a much larger run that is 7'x16' and 8' high. I was originally planning on using sand for my run, but the run is not completely flat, it's slightly sloped. Now I'm worried that all of the sand will just end up at the bottom of the run! Does anyone have a non-flat run and if so, what do you use on the ground?