Female Cat Spraying

Well spraying tend to be related to territorial insecurity (assuming no medical related issues). First of all ensure you have an appropriate cleaner that removes the actual smell for cats (normal house cleaner would not do, you need something to break down the crystals etc.) to remove that part of the incentive. Secondly look at reaching out to the local cat shelters to see who do CNR (Capture, Neuter, Release) programs to deal with the stray cat population. Once they are neutered this will reduce their marking and by extension the territorial threat so to speak. If you can also check your air ducts (outside) with a UV light (I've used this one which works very well for example) to see if they are marking in the area around your vent. If so you need to clean that area as well to avoid the smell coming in going forward (this can also be combined with an air guard or similar to ensure they don't pee there again if needed, check after a week to see if it's needed or not after cleaning and make sure there's no lovely soft stuff to pee in). If it still does not work trying putting a toilet there instead and then slowly move the toilet back to it's original location (and by slowly we're talking waiting two weeks and then moving it a few centimeters a day kind of slowly).