Other than hosing the area down, with perhaps a little soap, it's hard to get the smell out, eventually I would fade, the problem is that the cats will keep coming back and spraying in the same place, so someone told me once of this great idea and that it wouldn't hurt my plants, pour some cayienne pepper around the area where they pea, like me that was around the garbage pails, and in my flower garden. I put the pepper down, and they never came back again!....it burns there nose and sense of spell as too not be able to smell where they went last....It's not harmful to them or to you garden. Once they stop coming the smell will go. Buy a big jar of the stuff, cause when it rains, you'll need to re-apply. I buy the big jars in the 99cents stores.
well, good luck.
Sure fire method.
In the dirt areas of your yard, it best to remove as much topsoil as possible and replace it with new soil afterwards, about 3 inches or so. Spray entire area with mixture of 1 part vinegar to 2 parts water. Soak area very well. When it drys, apply baking soda liberally to entire area. I recommend getting a lot of baking soda, like a big bag 10 ibs, from a wholesale store. Let it sit it will wash away with the rain in a few days. Then apply the cayeene pepper as instructed from the answer above.
Just sprinkle some stuff they use for hamsters in their cages....the wood scrapings...the cats odor will eventually wash away from the rain etc.....
Why do you care if here is a little smell of cat pee in your back yard? It is natural out doors smell like evey thing but if you really want to get rid of that smell hose it down and stuff.