I've had that same problem and animal-lover that I am I did consider euthanasia, when my baby came along and the home was unsanitary. The cat belonged to my husband before we got together, he had three in all, but only one sprayed - furniture, floor, bed, fireplace, baby's soft toys - nowhere was safe and it was HORRIBLE, and extremely smelly. We talked to the Cat Protection League, but no-one had an answer that worked. We did not try getting rid of the other cats because my husband loved them all, and there was no guarantee that would work anyway. I was constantly on the alert, putting things out of his way, closing doors and crying. It actually gave me nightmares, in my hormonal state. We tried everything and nothing worked. We did try Feliway, sometimes you would think something had worked only to smell the stench once more, track down and try to disinfect. The thing is, animals are supposed to be our pets and enhance our lives, not bedevil them. In the end all we could do was have a cat shed outside, that we kept clean and dry and if I remember rightly we put a little garden heater in it. I do feel for you, there is no easy answer and in cold blood I could not take a healthy cat down to the vets to be put down, however much I felt like wringing his neck when he offended! It's a very sad situation. Now I've got dogs and they are much easier to train and communicate with! Good luck!