First off I would check to see why the culprit sprayed. Is it medical or behavioural?

Secondly, check to make sure that a bottle of amonia hasn't spilt in or near the garage (or hasn't been used for that matter) - a friend found that was why her cats were spraying (to mask the scent of the ammonia) on her garage door as she washed it with something amonia based. They had never sprayed before either.

She also found that was why they peed in the house where ever she cleaned with any ammonia based product!

It would be hard to tell which one sprayed since both will go and have a sniff at the mark. Thats a natural kitty thing.


Other than that - best of luck!