Oh you poor thing!!! I know how you must feel though. When Max was just a puppy, we lived where there was a HUGE back yard, mostly desert landscaping....so very dry. And some neighborhood cats apparently used it for their litterbox when they were on their nightly patrols.....I never noticed any of it, but every now and then, here Max would come trotting across the yard with a cat turd in his mouth
. It was the kind of place that there wasn't much you could do about it (we were leasing) other than just keep an eye on Max all the time.
Then, I have 2 cats who used to live in the laundry room (it was a 2 room affair, so they had LOTS of space), so Max was never around the litter box. And now, the cats have their own bedroom/bathroom and I put the litter box in the bathroom ~ if I'm not paying attention, Max is automatically in there nosing thru the litter box (after I've picked up their food dishes)...so I just have to really pay attention to him and not get distracted by anything else, LOL.
Is there a way you could maybe put up a baby type gate across the area where the litter box is...in a way the cats could get in but not the dogs?Or just something so that the cats could get in, but it would make it more difficult for the dog to get in and hopefully you'd catch him first
?
Luckily, so far I've mainly only had to deal with Max eating their FOOD....it seems to be a good deterrent to eating cat poop LOL.
Good luck!