Thanks for the replies. I do have one, "free," litter box in the form of a foot bath I bought and then never used. It's basically the same shape as a litter box. I only had one, though, and I need two. I did end up buying one with stairs and a slight curve. I figured it would add a slight challenge to the dogs trying to get into it. One litter box is only used when I'm at work and the cat's locked away (until he gets older), so the dogs don't get to that one. Hopefully the odd ball litter box and the gate I already have up will keep my dog's from sneaking any, "snacks." They are the size of an adult cat... so, unless someone invents a litter box that can sense animal specie, I have to stay creative.
I don't know if I need a new topic for this... but, can you put litter boxes on top of things (very steady things) and still appeal to a cat's natural instincts? When Siberious can jump onto large flat objects then the litter box and the roaming dogs won't be an issue. They have short legs and they are not jumpers at all. They can't even make it into the couch half of the time.