Scent marking in the house

[SquirtedPerfumeUpNoseInBoots]

We have had TomCat for about 4 years. Hes a rescue, so no idea how old he is, but approx 7 yrs. He is neutered. He has started reversing up to walls and doors and scent marking.

He's been checked over by the vet who could find nothing wrong, a sample was tested and no infection. Vet suggested stress so I've bought some anti stress drops to add to his food but after a week theres not much difference.

Yesterday I noticed him get very cross (fluffed up and hissing) with a new cat outside that Ive not seen about before. Its only got 3 legs so was distinctive. So obviously that will be the cause then.

He immediately came in and tried to scent mark inside the house.
No other cats have ever, ever been in the house, and we have no cat flap. Its not always the one room either. It can be the ensuite (upstairs) just as random as any other location.

I'm getting really fed up with it now, has anyone any ideas how to tell him inside is inside, and no cats here.

[Fluffycloudland77]

They need to sort out a hierarchy, sounds like this other cats dominant.

I don't think you can teach them about inside not being vulnerable to attack, as far as he's concerned he's telling the other cat that this is his territory.

It does settle down eventually.

[SquirtedPerfumeUpNoseInBoots]

Thanks Fluffy.

I hope they sort it sooner rather than later then. My cat is a big wuss.