Female cats that continue to spray after they have been spayed may have part of their ovaries left behind from when they were altered. Spaying a cat is effective at stopping female cats from spraying most of the time, but approximately 5 percent of cats continue to spray. Cats spray for numerous reasons, including stress, urinary tract infections, issues with their litter box and communicating with other cats.
When female cats spray urine, they usually spray on vertical surfaces and the urine will be extremely pungent. Cats that have litter box problems will produce more urine and it will not be as pungent. Cats also do not like any type of changes within a household, so they easily become stressed, which causes them to spray. Urine spraying can also be caused when there is any type of conflict between cats.
To deter cats from spraying in the house, it helps to move their litter box to the area that they normally spray. If the cat lives in a multiple-cat household, it's important that there are enough litter boxes in the house for all of them, preferably one litter box per cat, and one extra. It is also crucial to take the cat to a veterinarian to rule out any health problems that would cause them to spray after they have already been spayed.