Cats mark territory with small amounts of urine sprayed onto vertical surfaces, or clawing of surfaces which allows scent glands to mark the area, or with faeces. This is normal behaviour but when it happens indoors it is likely to be due to stress.

The kind of stresses that lead cats to mark indoors include the arrival of a new baby or other new person, and building work; but by far the biggest stressor is other cats. This may be other cats outdoors being intimidating (the intimidation may be invisible to the human eye); other cats in the household; or neighbouring cats which come in through the catflap and bully the spraying cat in its own house (the worst case scenario).

Any cat male, female, neutered or entire can mark with urine, and cats which are inherently anxious are most prone. Cats are often not comfortable living in the high-population scenario they find themselves in today, and countries where the cat population is lower or more spread out, report that urine-marking behaviour indoors is practically unheard of.

If you find small amounts of urine in a number of locations around the house a complete veterinary examination will be necessary to rule out potential physical causes. If the cat is not already neutered, and is not a potential breeder, then neutering is recommended.

If physical illness has been ruled out, then treatment is aimed at breaking the habit and decreasing the motivation for spraying.  This is achieved by paying attention to adequate cleaning and also by working to decrease stress and anxiety.

If the problem relates to cats outside of the home, then the best options are to find a way to deter the cats from coming onto the property or to prevent the indoor cat from seeing, smelling or hearing these cats.  Cat flaps may need to be locked, at least temporarily. It may be helpful to house your cat in a room away from windows and doors to the outdoors, or it may be possible to block visual access to windows up to the height of the cat.  When you are at home and supervising you can allow your cat limited access to these areas.  It may be necessary to keep windows closed to prevent the inside cat from smelling the cats outside, and you will need to use an appropriate cleaning regime to deal with those areas where the outdoor cats have eliminated or sprayed. 

If the problem is due to feline social interactions inside the home, it may be necessary to determine which cats do not get along.  Temporarily keep these cats in separate parts of the home with their own litter and sleeping areas.  Reintroduction of the cats may be possible when they are properly supervised and can be aided by allowing the cats together for positive experiences such as feeding, treats and play sessions whereby they get used to the presence of each other, at least on a limited basis, in a positive context.  However, when numbers of cats in a home reach 7-10 cats you will often have spraying and marking problems that cannot be resolved without rehoming one or more of the cats.

Where the problem is related to disruption in the household through renovation or redecoration it can help to keep the cat isolated from the worst affected areas, and where the cat’s anxiety is related to new members of the family in the form of a new spouse or a new baby treatment will need to include desensitising and counter conditioning the cat to the new arrival.

The cat should never be punished (even if it is 'caught in the act') as this is only likely to make it more anxious.  Placing food (dry food is best) or a bed at the base of spraying sites is often helpful at protecting those particular areas as cats are extremely reluctant to spray their own key resources, although they may simply move to other areas and mark there instead.  Food and beds are also reassuring and may reduce anxiety.