Your best bet is specially formulated cleaners that you can get at pet stores.
Natures Miracle found in pet stores works really well. Use a black light to find the exact area in which the doggie did his thing. It will glow green. As you spray the area and the odor is removed so will the green glow go away.
If you still have the glow, the odor will still be present.
Yes. Natures Miracle is the best ever. I've used it before on old urine stains and my dog could not detect where it had been after the process had finished. It can smell a little worse at first. That just means it's working.
will it work even when the urine or stain has dried up for a long period of time?
It did for me. I used it on carpet. The product consists of an enzyme that eats the urine. I guess it dies off after all the bacteria is consumed. That's why it smells stronger at first then goes away completely.
Yes it does Gynarchy B. Another method of removal of odors is Ozone. Ozone in high concentrations will remove many odors that you cannot find the source of. We use that all the time for foul odors in homes that we work in.
thank you all so much for your ideas.