Fortunately for me the horses are able to come in and out of the stall into the paddock as they please. Unfortunately, they like to pee in the stall, no splatter I guess!
Pick out every day, very little to pick, and scoop up the urine soaked shavings. They always pee in the same spot so that's easy. I haven't had to strip the stall ever, but I do rotate the shavings, by pushing the old shavings to the urine area and put down new shavings in the other spot. I go through about one bag of shavings every week to week and a half.
I have a barrier between the dirt floor and the shavings so that helps too. I use a vinegar and water mix to spray on the urine areas to help with the odor, have used lime in the past though.
I have only one very large stall for both horses, I believe its 12 x 16 and there's room for both to lay down, which they do.