Removing dog urine from carpet is a time consuming process because it soaks through the carpet and into the padding. Even with all of the urine removed, the bacteria in the urine seeps into the subfloor. This can make the room smell of dog urine once all physical traces of the urine have been removed. Urine and the smell of urine can eventually be removed with diligence and time.
Soak up all of the excess urine with towels. Pour vinegar over the area, including at least 2 inches outside of the visible stain. Allow the vinegar to set for a half an hour. Soak up the excess vinegar with towels.
Go over the spot with the steam cleaner. Use hot water and the carpet cleaner. If the steam cleaner has a heavy traffic button, use the heavy traffic button (this puts out more water and soap as it scrubs). Make sure you get the entire area, including about 6 inches outside the circumference of the stain. This step should remove the stain. If not, repeat Step 2.
Allow the carpet to dry. Allow humidity to enter the room---either by opening the windows or turning the heat on for a half an hour or so. Take note of whether you can still smell urine. If there is no urine smell, treat the carpet with carpet deodoriser. If you can still smell urine, continue to Step 4.
Pour vinegar over the spot again. Allow the vinegar to set for a half an hour. Using the steam cleaner, go over the spot (do not soak up the excess vinegar with towels this time). Make sure the water is hot. Run over the spot until the vinegar is sucked up. Once sucked up, if you run over the spot without pushing the soaping button, the steam cleaner will soak up most of the liquid, partially drying the carpet.
Apply carpet deodoriser. You may still notice a smell once the deodoriser dissipates. Run the steam cleaner in normal mode over the spot. Apply carpet deodoriser. It may take three or four separate times to get all of the smell out of the carpet, padding and subfloor.
You can also use any of the chemical urine-gone type products on the market instead of vinegar. While vinegar does leave a lingering smell for a bit, the carpet deodoriser generally overpowers it.
It may take several steam cleaner treatments to remove all of the smell, but should only take one or two to remove stains.