My guess is if the smell is that strong, that there may some some spots you haven't found and treated. Try using a black light at night with all the lights off and see if that's true.
Then enzyme the heck out of any spot that shows up under the black light. Shampoo the carpet well, let it dry, shampoo it again - this time add some enzyme to the cleaner (see bottle instructions) and let it dry. You may have to shampoo several times to get all the pee out. When you shampoo and the wet carpet doesn't smell like pee, you're in good shape.
I don't know that anything takes the smell completely away, but this does a pretty good job of it. Then you have to stay on top of the spots they pee in. If they aren't crated or restricted while you're gone, it's going to happen over and over. I highly recommend restricting them to one area that's not carpeted if you don't already.
I have a handheld steamer-vac that I use as soon as I can on accidents. it was a good $30 investment on eBay. Plus I shampoo frequently. Hope this helps - I know it sounds like a lot of work and - yep, it is!
