I've had this problem for months too... we had an aggressive un-neutered tom barging through the magnetic cat flap and spraying every where (I have three spayed girls) - even upstairs over tbe bed clothes, school bags, shoes, even the bread crock on the floor, laundry heaped on the floor, then someone would walk through it unwittingly and then it would end up tracked through to the bedroom carpets .....uugh! What has helped is getting hold of him and his owners and taking him to the Vets and paying to have him neutered.....Hooray... two whole days without pissy smells... until .. yet another tom opportunistically barged in and marked HIS territory as well..

I was using a plant sprayer with slightly diluted vinegar and ultra-concentrated disinfectant to spray everywhere and wet it thoroughly and then going around with 'Neutradol' which is an odour neutralising room spray. Do you get that in the States? The combination of these two processes seemed to work fairly well.

Please God, fingers crossed, what's keeping them out now is leaving the door curtain pulled, so once they get through the cat flap they would have to fight their way past the heavy curtain. The 'girls' seem to cope with that alright - and despite (today) 4 toms sitting outside they haven't found their way back in yet..