Cement is a porous surface. If a cat pees or marks on concrete, the urine smell is stubborn and long-lasting. Before trying one of the pricey commercial pet-odour removal products on the market, look in your kitchen cabinets -- you probably have what you need to get the urine smell out of concrete already. The trick is to saturate the concrete with something that neutralises the smell instead of merely masking it.
Turn off the lights or wait until dark, then shine a black light over the concrete. Urine on concrete is difficult to see and the black light will make it glow pale green. Purchase a black light bulb at any hardware or home improvement store.
Saturate the urine with a mix of equal parts water and white vinegar. If it's on the floor, pour a liberal amount of vinegar over the area. Use a spray bottle filled with the vinegar solution on vertical surfaces that a male cat may have marked with urine.
Blot up the excess vinegar with paper towels or absorbent rags.
Sprinkle baking soda over the area. Pour a mixture of hydrogen peroxide with a little dishwashing detergent over the baking soda until you have a paste, and scour it with a scrub brush. For vertical surfaces, mix the three ingredients into a paste and apply to the stain.
Allow the paste to dry. Sweep, vacuum or hose away the residue.
Pet stores and most hardware stores carry commercial products designed to remove pet stains and odours.
Do not use bleach on urine stains. The New Jersey Department of Health warns that mixing bleach with urine will create toxic chloramine gas. Don't use ammonia, or any cleaner containing ammonia, to clean urine. It will smell like urine to a cat and will tempt it to use the same spot again.