I have wood shavings in the coop but fill my run with leaves every fall. And I mean fill. The leaves are at least 12 inches deep. The chickens sometimes look like little periscopes as all I can see is their heads as they walk around. The chickens love it and are busy for hours rummaging and diving through the leaves. I also hope it helps to keep them warm in the winter. I save bags of leaves and every few weeks over the winter replenish the leaves as they break down quickly. There is no odor. In the spring I rake the leaves out, dump them in the compost and add a new thick layer of sand to the run. We have lots of trees (oak, maple, locust, ash, dogwood, pear...) and this system works well for the chickens and for us.