There's a new litter out that is made from corn. I haven't tried it but it is supposed to be really good for odors. I'll see if I can find the name of it.
You might want to talk to your vet. This may not be a litter problem but a kitty problem. I have two indoor cats and one needs an enzyme additive for the food (both cats eat the same food!). Otherwise, I could box her up, send her to the military to be the new secret bio-weapon. We call her a Sassy bomb. Very hush hush. :-)