I have 6 cats and currently have 8 litterboxes. All but 2 are uncovered. I've been using the feliway plugins as well as the spray for about 3 months now and it's helped a lot. I also bought cat attract litter at Petsmart. As far as I know they're the only retail pet store that carries it. I just added it to the top of my old litter and it worked great.

Now I don't even have to use it because everything has been resolved. Dr. Elsey also sells precious cat ultra scoopable litter that also works well for later use.

I also use the simple solution enzyme cleaner and it's been working well for me. I hope that something will work for you. Good luck.