I don't have any sand in there. It is just bare dirt, and it slopes 5 to 10 degrees. I now have three terraces which do a great job of limiting erosion. My run never stinks, but it is large @ 1900 square feet and for 10 layers currently.
I suppose really flat runs can smell. I don't have any ideas really, except to increase the size. The rain must take all of the odor away in my case. My coop never stinks either. But in the AM when I open the pop doors and go in to scrape the poop boards I can smell the poop. The odor vanishes in minutes after I finish cleaning the coop each AM. It takes me around 3 minutes total each day. We use the deep litter method and I use grass clippings for litter.
I do put in a ton of coarse sand each year for a path from the gate to the coop so as to prevent either of us from slipping and falling in rainy weather. I also doubles as grit for the chooks being as they can pick out the sizes they want to swallow. I always get the coarse sand from the crusher. It is the same stuff used in concrete, minus the bigger pieces of gravel.