If you have gone thru all the fixes, the wax seal, vent pipe, bathroom fan, etc. Make sure at some point that you check the toilet flange and pipe. In older homes with cast iron pipe, there was sometimes a lead flange used, which can "rot" out. If it is plastic make sure that the pipe was not broken at some point. It may be time to call in a plumber. If everything is OK then the urine has seeped thru the tile grout into the concrete. Not much you can really do, You may try an oder eliminator available at a large pet store.