I know how frustrating animals can be.
I have cats also and we had a similar problem with the current dog. The dog is one of those poop eaters and used to go diving in the litter box for "toasted almond bars".
Tried everything, tabasco, bitter apple, the dog liked it even better.
Putting the litter boxes in a place where the dog could not get to it was not an option so I found litter boxes with openings that the dog could not get her head through but still allowed the cats access.
I'd try scat mats, they give off a mild static charge and can be moved from place to place.
http://futurepet.com/cgi-bin/fullpres.exe?PARTNUM=SKM411&GO=G1
Another option, is your house configured so you can use a baby gate to block of access to the kitchen?
My point with the kids is that my 4 year old kid is smarter than any dog but you still can't trust them so the safe thing to do is remove temptation whenever possible. There are certain things that we can let them learn through experience, like not touching something hot, they understand that one first time out. Other experiences can kill them 1st time around so better to be vigilant than not.
True story, as a kid I stuck a metal rod into an outlet. Curiousity nearly killed me.
Good luck,
Scott