When Cats Stop Getting Along: Tension, Spraying and Multi-Cat Homes
The call came from a client in Norwood about two cats who'd lived together for five years without incident and had, over the course of about three weeks, started blocking doorways. Then the urine started, on the sofa and on a school bag by the front door. The owners had already bought a diffuser, a spray and two collars, and nothing had shifted.
I asked one question before anything else: was either cat limping, hiding, or off their food? Yes, slightly. That's a vet appointment, not a behaviour consult, and it turned out to be early arthritis in the older cat. Pain makes cats defensive, and defensive cats guard doorways. Every product in the house was aimed at a problem that was actually a sore hip.
Rule one with cats is always medical
I'd guess that close to half the multi-cat cases I see have a medical component, and it's the reason I now insist on a vet check before we talk about anything else. Urinary tract disease, arthritis, dental pain and hyperthyroidism all change how a cat behaves towards their housemate, and all of them are more common in the age group where these problems usually start.
Toileting outside the tray gets treated as spite, and it almost never is. It's either a medical problem, a litter tray problem, or a territory problem, in roughly that order of frequency. Ruling out the first two is quick and it's where I start every single time.
Then the resources, and be more generous than feels necessary
The rule is one tray per cat plus one, in different locations, not lined up in the laundry. Then the same logic applies to everything else that can be contested: food stations, water, resting spots, and — the one people forget — routes. If a cat can only get from the kitchen to the bedroom by walking past another cat, that's a flashpoint, and no product fixes a floor plan.
Vertical space is the cheapest intervention I know. A shelf, a cat tree, a cleared bookcase. Height gives the more anxious cat a route that doesn't involve going through anybody else's space, and in a lot of houses that alone takes the edge off within a fortnight.
Where a collar fits, and where it doesn't
Once the medical side is clear and the resources are sorted, a collar can genuinely help in a multi-cat home — but it works best as a pair rather than one. Putting a collar on only the anxious cat leaves you with one calmer cat being bullied by an unchanged one, which is not obviously an improvement. I usually suggest both cats wear one, so the overall tension in the house comes down rather than the balance shifting.
Expectations matter here too. What a collar can do is lower the general level of reactivity so that reintroductions are possible. What it cannot do is resolve a territory dispute on its own. If two cats have been fighting, the actual work is a proper separation and slow reintroduction, and the collar is background support while that happens.
The reintroduction, briefly
Full separation: separate rooms, separate trays, separate feeding, no visual contact at all, for at least a week. Then scent swapping, by rubbing a cloth on one cat's cheeks and putting it under the other's food bowl, so the smell arrives with dinner. Then feeding on opposite sides of a closed door, moving the bowls closer over several days. Then a crack of visual contact during a meal, behind a barrier, and if either cat stops eating, you've gone too fast.
The whole process takes weeks and the most common failure is speed. People see two cats eating calmly either side of a door and open it on day three. I've done it myself and it cost me a fortnight of progress.
A note on the products themselves
If you're shopping in this category for cats, read the species statement on the label rather than the picture on the packet. Cats process many plant compounds differently from dogs because they lack a particular liver enzyme, so a collar formulated for dogs is not the right starting point for a cat, whatever the packaging suggests.
Keep rooms ventilated, respect the stated minimum age, and take it off immediately if you see drooling, wobbling or any skin reaction under the collar. And whatever the advertising implies, a collar supports relaxation. It doesn't resolve conflict, and any brand telling you it does is overselling.
The Norwood cats were sharing a windowsill again six weeks later, mostly because a sore hip got treated and a bookshelf got cleared. The collars helped. They weren't the thing that fixed it, and I'd rather tell you that now than have you find it out after three weeks of diffusers. — Nadia, Adelaide, with two cats who have negotiated a truce.
Frequently Asked Questions
Why is my cat suddenly toileting outside the litter tray?
Work through three causes in order: medical, litter setup, then territory. Urinary tract disease and arthritis are very common and very treatable, so a vet check should come first, particularly if the behaviour appeared suddenly.
How many litter trays do two cats need?
Three, in three different locations rather than grouped together. The same logic applies to food stations, water and resting places. Competition over routes and resources is the most common driver of tension between cats.
Should both cats wear a calming collar?
Usually yes. Collaring only the anxious cat tends to shift the balance rather than lower overall tension. Both cats wearing one brings the general reactivity level down, which makes reintroduction work possible.
How long does reintroducing two cats take?
Expect several weeks. Full separation for at least a week, then scent swapping, then feeding either side of a closed door, then brief supervised visual contact. If either cat stops eating, you have moved too quickly.
Can a calming collar stop cats fighting?
No. It can lower general reactivity so a reintroduction is easier, but it will not resolve a territory dispute by itself. If cats are actively fighting, separate them fully and get veterinary advice before starting a slow reintroduction.
Size & Fit Reference
| Size | Neck circumference | Collar length | Typical pets |
|---|---|---|---|
| Cat | 18–25 cm | 38 cm | Cats, kittens, toy breeds |
| Small | 25–35 cm | 45 cm | Puppies, Cavoodle, small terriers |
| Medium | 35–48 cm | 62 cm (cut to fit) | Kelpie, Cocker Spaniel, most adult dogs |
| Large | 48–62 cm | 65 cm (cut to fit) | Labrador, Greyhound, large breeds |
Most collars release for around 60 days once the sealed pouch is opened. Replace every eight weeks, or sooner if the scent fades.
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