We are building a run for our girls on the side of our house. Right now there are rocks/gravel covering the ground. We are going to move the rocks, leaving dirt as the ground of the run. They have been in our yard with grass for the past 4 months. Will the dirt be good enough for them or is there something else you recommend putting down on the ground. The area doesn't get a whole lot of sun, so we don't think grass would hold up well.