Hi and welcome to PT. I've had to use Dr. Elsey's Cat Attract Litter before due to peeing issues and it worked right away for me. My vet recommended it and all I had to do was to put some of it on top of the litter that I was using at the time. You can either buy it online or at Petsmart. I guess they also make a Kitten Attract litter now too.

I now use Dr. Elsey's Precious Cat Ultra Litter which is unscented clumping litter and both I and my cats love it. I have both uncovered litter boxes and a few covered so that my cats have the choice to use the ones they prefer. I use the pet enzyme Simple Solution which you can buy at most pet stores. I scoop at least 2 times a day. I hope that you'll be able to solve this horrible problem once and for all. Here's an excellent link to help solve litter box problems: http://www.catinfo.org/?link=litterbox. Good luck.