Your first challenge is to find all the contamination and this usually requires using a combination of your nose and a black light. One of the best ways to find exactly where a pet has urinated is to buy a black light and not all black lights will work. We have found fluorescent to be superior to incandescent. Wal-Mart sells one that is about 18 inches long and has a fluorescent tube in a black housing for about $20. Or, if your Wal-mart doesn’t have the complete unit you can buy the tube separately and purchase an under-the-counter fixture that the tube fits in. These are also available on Amazon. Pet stores generally want over $30 for a much smaller light that doesn’t work as well. Pet urine will show up as a yellow stain under the black light on most surfaces. All pet urine has a very low surface tension, which means that it penetrates deep into every miniscule pore of whatever surface or material you are treating. Odor Medicine O.F. Concentrate is designed to penetrate exactly the same way and we recommend that you use a common pump-up sprayer that is available at any hardware store to apply our products. This allows you to apply it efficiently and to be able to inject it under pressure behind walls and other areas that are not easily accessed. You will find that cats will urinate on furniture, beds, just about anywhere, but in most cases all the contamination will be within 3 feet of the walls or whatever vertical surface is close to the wall…..like a dresser or a bookcase. Dogs on the other hand generally urinate at random all over the place. Do a good job at finding ALL the contamination because it doesn’t take much pet urine to stink up your entire house!