I had a problem with my cat marking when we moved into our new house.
She would pee right next to her box on the tile floors. It would get in the grout...gross!!!
I love my kittie but there is nothing more rancid than the smell of cat urine!!!! I thought is was hopeless...anywho...Walmart carries this amazing product called "Kids 'N' Pets.
It is a stain and odor remover. It works wonders!
I would get a bottle of that and put it on the spray area and get a little dust broom and brush it into the pores of the concrete. That should get it out. This stuff works on carpet too!!!!
My sis got intoxicated one night and peed and threw up in her husbands BRAND NEW TRUCK
...She went and got this stuff and it was like it was never there!
Good luck!