You can put sand in your run. My run is rather small (50 sq.ft.) and in order to have about 4 to 5 inches of sand inside it, I shovelled in about 600 kilos (1 300 pounds) of sand.
Then, you could make a big campfire and the next day, dump all the ashes inside.
It's a very interesting way of doing things because the run is clean, it is easily cleaned and you don't lose feed in a huge mess.
I now simply throw the feed all over the run. Thus, the hens walk around, scratch, hunt and peck and sort of "work" for their food. For the sake of variety, I also throw in a few handfuls of grass clippings, clover and other good stuff.
The hens can also enjoy dust baths.