How to deter male cat from spraying at door?

[theyremine]

About 5 weeks ago my bonded  former ferals started to fight; rather the male began attacking his sister.  It got so bad he actually scratched her ear (and left a scar) at one point.  I have had them separated for the last 3 weeks after efforts to reintroduce them failed.  Talking to others to try to find a cause for the change in their relationship, redirected aggression was mentioned. (Both my cats are spayed/neutered)  Yet I haven't seen a stray/feral in the past couple of years since coyotes have been seen in the area.  Up the street there is an indoor/outdoor cat who appears to be well cared for.  I don't know if the cat is male or female.

But today, I definitely smelled strong cat urine outside  the back door.   So perhaps the redirected aggression theory is correct.   So how do I keep this cat away from my door/house and hopefully restore peace in my household?

 

[mani]

I've had the same problem with a neighbour's cat marking its territory. My cats definitely had a bad case of redirected aggression (it doesn't take much for them.. they're at each other if I don't feed them on time. 

)

  I cleaned the area really well with an enzyme cleaner (if you don't clean it, nothing will stop them from respraying).  Then I used one of the cat deterrent sprays on the market (I'm in Australia so it's best to look up what is available in your area).

I also asked my neighbour whether the cat was spayed.  He was relatively young and wasn't.  Luckily we get on OK and they trotted him off to the vet.