The concrete floor in my garage had been home to a large dog for several years. There is a visible stain and strong smell in one area of the garage floor. The concrete does not appear to be sealed or painted. What is the best way to remove the odor?
Let me save you some time. Forget the pet store products, just go to Home Depot or Lowe's and get yourself a can of primer/sealer, I think Kilz brand is the best.
I had a really bad cat urine odor problem in my townhome many years ago (from previous owners). Like you, I went to the Internet and I tried a lot of suggestions I found there. NONE of those specialty pet odor removal products worked. They just temporarily covered up the smell and during hot weather it came back. Big waste of money and time.
Finally someone suggested the Kilz brand primer/sealer and it worked. The smell never ever came back, and there was a clean "new home" smell. I used it on drywall but I'm sure they have stuff for concrete as well.
I use Anti Icky Poo: http://antiickypoo.com/ It works great. It's important to remove the odor to prevent repeat offenses. I recommend blocking the area off for a few months in addition.
You could also try Drylok, http://www.ugl.com/drylokMasonry/masonryWaterproofer/latex.php. You probably won't be able to remove anything that is causing the odor in the concrete so I'd try to seal it in instead. I believe they also sell something that will etch the surface of the concrete so the Drylok will adhere better.
I haven't had any luck with enzyme products once the stain is dried and set-in over a long period of time.