I use Arm and Hammer cat box spray. It's intended to keep the urine/feces odors down on cat litter, but it works FANTASTIC on carpets. I spray it straight up in the air and it doesn't take long to clear out the smell
I use it on my mouse tank too. Granted I only have one, but she can get herself into a right funk. Works awesome
Its in the cat aisle at Walmart, and I'm assuming anywhere else that carries cat litter.