My run is on top of concrete (no where else to put it). Have been using sand for the last year. Bottom layer continually gets stinky and I have to remove it all and start fresh every couple months. I go through and pick up poop weekly. After this weeks rain storm, I am going to remove it all and start fresh. Tried putting in some lime and PDZ refresher and nothing helped. Would I be better to use a soil/sand mixture this time? If so, what type of soil would I buy at lowes/home depot?