My grandparents have a boarding stables with 78 horses. For mud, the only way to control all the divots was bring in hog fuel, about 4-5' of it on top the dirt. For pastures, we have several runs, typically 3-6 horses per run, they all have their buddy groups. We always just haul the manure off to a local farmer and there is no grass that needs to be mowed in the pastures, it is all hog fuel. Were talking over an acre of barns, on a 4 acre piece of land. At my dads I actually don't like using the chain harrow. The manure dries up so much that it just wont spread out well, you just use your bucket and slowly dump and drive forward at the same time. Our horses seem to like standing in the same spot their whole lives, i have to go out with the tractor quite often to scrape the mud back.