What kind of sealer to neutralize cat urine on concrete?

I have already used Nature's Miracle and Urine Off to try to get rid of the cat urine odor on concrete in basement. I need to use a sealer to seal in the remaining odor. I want a clear color. Do I use oil based or solvent based or what? I asked at Lowes and the folks there had no idea what to use for this problem. Any help is greatly appreciated....it is not for the floor...it is a cement ledge. thanks PS: If you have had success with anything- I'd love to know...very concerned about the odor.