I now have one cat, Meg and she is over 16 stayes inside mostly. My problem is strays and feral cats, possums etc that urinate on my deck and rockery.
I desperation I went to the local pet shop and they suggested a product called 'Urine off' deters the animals and gets rid of the stink. cost me about $30 AU (larger spray bottle) but worth every cent has lasted for two years and just about all my friends have used it.
possums love anything citrus. The possums usually spray on my army gear when out bush with our army cadets. Now I take some spray with me cause isn't anything worse than possum smell in the tassie Summer.