the best thing i have had that works with unwanted odours, i.e. sick etc, has been soda crystals. I would try these and they get rid of all kinds of smells and very easy to use.
Hi Silverstar wash the carpet with bio washing powder first. ( I do not mean pick it up and wash but use it in a bowl of water and a floor cloth) and then get a plastic spray bottle with water and put some surgical spirts in it, I put quite in. then spray the carpet with it. when it dries it should take the smell away. Then I just spray it every day until it has gone completely. good luck.oh by the way it will put the dog off the scent to do it there again.
Check that it hasn't soaked through under the carpet. If it has, however much cleaning you do with the carpet, if the floor underneath isn't addressed, then the smell will eventually come back.
Jeyes fluid on the floorboards or concrete floor may do the trick!
I've had several (intact) male cats. Their urine smells far worse than anything dogs can produce (and they have a nasty habit of spraying it everywhere!).
After trying all sorts of things to get rid of the smell, I finally discovered the 'Simple Solution' range of products. I can thoroughly recommend them. For dog urine, the product you want is this one: http://www.simplesolution.com/products_uk/stai n&odor.htm
It should be available at your local 'Pets at Home' store.