How about feeding a species appropriate diet. Scooping litter boxes daily. Washing boxes once a week. No smell and a healthier cat!
I have had people in and out of my house a lot this week. Many assumed our home would stink. (They fessed up later.) They ALL (even the ones with cats) were shocked that we have 6 cats and our house wasn't smelly. And there is no getting away from litter boxes in our home! No matter what room you are in, a litter box is close by.
I get so frustrated with carp that masks litter box smells. You won't have any, if you just do the RIGHT thing!