I feed fermented feed, so the chicken poop doesn't smell like much anymore and it doesn't attract flies any longer. You can put your nose right down to it and barely catch a whiff of anything resembling poop. I'm so loving this FF!!! Even when I had 54 broilers in this coop you couldn't smell a thing and no flies were around in 98* heat and high humidity. My ol' Ma was amazed...that sure wasn't how chickens smelled in her day!
Then I use deep litter that doesn't ever get cleaned out, just added to and it composts in place which absorbs all the nitrogenous droppings and sort of digests them into the soils below. You can pick up a handful of my bedding and not smell much but dirt.
I use leaves, pine needles, pine shavings, small twigs and anything else that gets raked up in the yard...you can find deer bones, possum teeth, deer hair, feathers and an old turtle shell all buried in this compost. This coop consumed 4 32 gal. trash cans of compressed leaves this winter, plus several piles raked into the coop in the fall and hay residue, pine shavings, etc. The bedding is currently only 6-8 in. deep...the composting is working right along.
I don't use DE or any such in the coop as I don't want to kill any beneficial, predatory bugs that prey upon parasites and their larvae. The composted bedding is a great place to breed your own mite and lice control.
I also have a coop with tons of ventilation...you really can't ever have enough ventilation. I have an open air cattle panel hoop coop, so the air does flow!
My chooks have been living in this coop in its present location since last Oct and the bedding is the original bedding that has been built upon and you can't tell that chickens live there. No smells, no flies.