If you are talking about a hardscape area that is non-porous, like concrete or rock, and don't have to worry about runoff damage, you could try bleach diluted in water at a rate of about 1 part bleach to 10 parts water.
Also spreading the soil with Pelletized lime will eliminate the odor.
Our concrete area has the smell of wet dog everytime it rains. They told us muratic acid. Make a bucket full 1 part acid to 2 parts water, we scrubbed it in with a stiff brush attached to our broom handle. Rinsed it. Still faint smell. Will repeat process. Then seal or paint concrete to keep it out.
Sorry for chiming in a bit late to the discussion, but I really feel like I need to add my 2 cents.
I know how frustrating it must be for you if you have a dog that just won’t learn how to potty outside. You’ve probably tried all sorts of training techniques that you found online or in a book at the library and nothing worked. At least, that’s what happened to me...
Me and my hubby were able to find a solution and I’ll always be thankful that we did, because since then we have had no problem teaching my foster dogs where to potty – and I can do it within a couple of days.
I now recommend it to everyone because it works so freakin' well and we save SOO much money!
Don't waste time sister! The more times your dog goes to the bathroom inside your home the harder it will be to break him of this habit.
Take action now and permanently stop your dog from using the bathroom inside before it's too late!
Here's the guide we used that shows you how to completely potty train any dog or puppy quickly and easily in 7 days or less...
No I have not been paid for this post nor do I make any commissions off of it. I really just want to help you guys out. I hope you don't mind.
I'm based in Sweden, by the way, so you should be able to get it too.
Good luck with the odor and the stains! It really lowers your quality of life, doesn't it?