Hello,
It’s important to distinguish between house-soiling and urine marking. Given the number of litter trays you have, your rigorous cleaning routine, and the fact that your cats are still using them, we can probably rule out standard house-soiling. It sounds more like marking, as you suspected. To be sure, check your cat’s posture (tail held high and quivering), the appearance of the mark (usually on a vertical surface, and more oily and pungent than normal urine), and the volume of urine (usually just a small amount).
Urine marking is a method of scent communication for both dogs and cats. Usually, it's only a temporary issue, but stress or changes in the environment can cause the behaviour to persist: a new pet or a new arrival in the home (like a partner or baby), moving house, a sudden change in routine, or being away for too long... There are also medical causes, such as urinary tract infections, but you mentioned you’ve already ruled this out with your vet.
There are several possible solutions: neutering your cats is the most effective method and the most likely to put an end to the problem. As the results aren't always guaranteed, you could speak to your vet about chemical neutering (an implant); this allows you to see if castration will have the desired effect before going ahead with surgery. Regardless, the procedure will at least help reduce the smell of the urine.
If your cats are marking near windows or areas where they can see outside, it might be because they are trying to interact with other cats they can see. You could try limiting their access to these spots.
Alternatively, there are pheromone diffusers available which are meant to make cats feel more at ease in their environment.
As I mentioned, stress could be an explanation for this behaviour, but since both your cats are doing it and it’s “only” marking, I think this hypothesis is less likely. However, in cases of chronic marking, if you’ve tried everything else, it would be worth making an appointment with a specialist veterinary behaviourist.
In the meantime, cleaning up the marks is key to limiting or stopping the behaviour. Clean up the urine as soon as possible to prevent the pheromones from soaking into the surfaces. I recommend using specific enzymatic sprays to break down the pheromones and avoid attracting your cats back to the spot. Most importantly, do not clean with bleach, as cats are strongly attracted to it.
I hope these tips help you get to the bottom of this chronic marking.
Best regards,
Quitterie
