We're deciding where to put our coop & run. We'd like to put it in an area of the yard that previously had pieces of broken glass. We've cleaned it all up, but there are gazillions of rocks, pebbles, and small pieces of broken concrete and twigs & stuff...is this okay? Will they eat the rocks? There are also some type of prickly bushes in there...maybe roses or raspberries? Those will be easy to pull out if they're a problem.