well, while your question isn't strictly a gardening question, it is one that gardener's seem to have more experience (and problems) with than most.
on that note, here is my 2 cents worth. my sister-in-law lived in el paso for several years, and to keep the smell from being an issue, she regularly scraped the dirt in the back yard (the dog's home) in areas that the dog used. that dirt, she would dispose of in the garbage. she included the the dried fecal matter in the garbage, in fact, that was the reason she did it, but it kept the urine odor down also.
additionally, if you aren't worried about soil ph (ie - not trying to grow a garden right there) you can pour vinegar over the areas that smell the worst as the vinegar will neutralize the odors. (kind of like you would use on a carpet spot in the house). finally, what i have done, and am still doing, is getting the large bags of cedar shavings/sawdust that is sold for small animal bedding, and spreading it in the dog yard. keeps the smell, the fleas, and the dust down. hope this helps, let us know how you make out!