Deep breath, new plan...

We found dabs of poop in the living room window seat, a dab on the floor and a pile in my craft room on the carpet.  So, we're taking a deep breath and forming a new plan.  The next mess of any size we find, one cat gets locked up. We're pretty sure it's Sassy so Sassy will get locked up first in my craft room at night.  We are also stopping the evening feeding.  We'll leave the dry food down but no wet food after early morning.  All the messes have occurred at night with the exception of one so we'll start with Sassy, lock her up when I go to bed and let her out in the morning.  If we still find messes in other parts of the house at least we will know who's doing it.  Sadie used my craft room box this morning and her elimination was round and firm, what I found on the carpet was fairly soft and runny, leading me to believe it was Sassy.  If we have to, we'll keep Sassy locked up until she's regularly going in the litter box again.  It's beginning to look like the closer the cats get, the more messes we have.  We're not having any fights or altercations, this morning they were both next to my chair, Sassy on the footstool and Sadie on the floor below it.  I've been playing with both of them regularly and we often show them affection.  I can't pass either one of them without rubbing ears and I have the scars from Sadie to prove it.  We're saddened to think we have many more years of trying to solve this problem and since both cats are relatively young that seems to be the case.  Where is the "Cat from Hell" guy when you really need him?