Even the tiniest residue of a small urine stain on the carpet or flooring  encourages your dog to continuously re-mark that spot. Unfortunately, many urine stains aren't always obvious, especially on dark carpets.  Under the ultraviolet light of a good UV black light, dried urine crystals are easy to see.

What you will need to find the stain

Make sure that the urine stains are dry, because WET URINE WILL NOT GLOW OR FLUORESCE under any black lights. So if you suspect your dog peed a few hours ago and you don’t know where, then you need to wait sufficient time for the urine to dry.

OK, so now you are ready to start:Turn off the lights, close the shades and shut the door. Ultraviolet light illuminates and shows urine most effectively when the room is completely dark. The darker the room, the easier it will be for you to locate those sneaky urine stains.Put on your  UV  safety glasses, to protect your eyes from the ultraviolet light and help you see the stains when using the light.

Turn on the flashlight and scan the carpet. If using a inexpensive (under $15) blacklight, then likely you will need to hold the light about 12-18 inches above the floor (stronger UV flashlights will allow you to scan a room from 10 ft away).

Keep in mind that ultraviolet light will turn food and fluid stains various shades of fluorescent white, blue or green. Urine stains, however, are not always bright. Urine crystals are dull in color, and will appear as pea-soup green or brownish-yellow.

Confirm that the spot you found is indeed urine with the ‘ smell test’ (not scientific, but it does work!). Urine, of any type or age, has an odor that is unmistakable.

Once you've confirmed that the stain is indeed urine, stick a small piece of masking tape on the center of the stain so you know where to concentrate your cleaning efforts. For larger stains, use several pieces of masking tape to mark the outer limits of the stain's perimeter.Masking tape

Tips

Repeat this process a few days after cleaning to make sure you cleaned it thoroughly.  Older and deeper stains often require multiple cleaning sessions before they're completely gone.

When cleaning and you saturate the stain with cleanser, start a few inches outside the perimeter, and work your way toward the center. Urine spreads under the carpet padding, which means you must clean a space slightly larger than the stain.

Don't let your dog on the ‘cleaned’ carpet until you've confirmed that you completely removed the stain. Your dog's strong sense of smell will allow him to find and mark even a trace of urine hiding deep in the carpet. Consider using ‘bio’ cleaning products to help remove any traces of the urine on the spotted areas

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