Are your males neutered? If they aren't then the smell is enough to burn your eyes out. If they are neutered then someones just got really strong pee and as Deja said is marking. I use a littermaid box but I only have two cats, I think it works great. I was afraid of bringing the second cat in that if the litter wasn't clean at all times I would face the same problem you have now. With multiple cats it really doesn't make it more convenient since I still need to clean nearly everyday but it keeps the kitties happy with a clean box everytime.