We opted to go with leveling the clay soil and putting our mats over the top of that. That worked out great through the winter, but our last two big rain storms (this last one is the one causing all the flooding in Louisville right now) has wreaked havoc on the whole situation out there and I have decided it's time to try something different. Right now, I think I will be going with a bed of crusher fines 4-5 inches deep, compacted and matted over the top of that. I suppose I am most looking to hear from anyone who has used crusher fines - are they really all they are cracked up to be for a "sub-floor" for stalls? It seems to be the hot ticket for people out here, but is not something I have encountered using where I lived before.