Well, I don't have 10 litter boxes, I have 3 large ones in the house and 3 in the cottage (4 of my 14 are just 9 months old). As far as ruling out any medical problems, that's tough. What we did do today was buy a security camera. My husband is mounting it where we have the biggest problem. If we find that it is always the same cat or cats doing the inappropriate peeing/spraying, then that will be the one who is checked by the vet. Last fall I did take 2 of the cats that I had caught peeing to the vet. One did have crystals and was treated. It's just hard to imagine that so many would have medical issues. Also, all have been spayed/neutered.