Once a year!!!! Whats your secret pray tell? Deep litter bedding you say. I use layered straw and change it about every 3 weeks. The coop smell and odor almost dictates when it is time to change it. I have 23 birds At 4 months old. Lots of poo! I'm all ears!
There are excellent threads on DLM coop management. But the jist is to use at least 4 to 6 inches of hay chopped or straw (hay works better as it is more absorbent). When the poop gets pasty on top then you stir and flip the bedding and add a layer as it packs down. If it gets too glazed then you can skim off the top layer and add a layer back. You can also add DE to the floor and intermittently along with hydrated lime (any kind will work). Make sure you mix in the lime as it may cause mild irritation to young chickens feet.
As the litter bed gets thicker you may have clearance issues and need to skim off a few inches. Some DLM folks have as much as 8 to 10 inches on a regular basis. The ammonia problem comes from a lack of ventilation. Remember, drafts bad below or at head height on the roost. Ventilation is a must and I suspect that the folks having smell issues are actually ventilation issues. OPEN up that coop to exchange the air all the time. Chickens can keep themselves warm as long as their feet and combs don't get frostbite or dampness (seen as condensation in the coop or the litter bed). With the DLM, you get a benefit of added insulation in the best spot for chickens.
Bed, poop, stir, add, skim. It is that easy.