dog urine carpet

How do I get rid of dog urine odour in carpet?

I have a weimaraner from a rescue centre who is absolutely gorgeous, he had been castrated previously, we have recently heard that dogs who have had this done tend to scent inside the house as well as outside. We try to stop him when we see him do this, but obviously when we go to bed or go out, no one is there to stop him from doing this. How can we stop him doing this and how do I get the smell of dog urine odour out of the carpet. I have tried Listerine and pet products but nothing seems to work. Any ideas that have worked please, otherwise it looks as if I will need a new carpet. But then the same will happen all over again.

I use the hoover carpet cleaner. That machine was the best $200 I ever spent. The cleaner that comes with it works wonders. My dogs went through a peeing stage too.