Cats have been bullied for 3 years

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My girl cat now refuses to go out.
My boy cat goes out but is reluctant and when he does I hear the bully cat screaming at him
The cat will sit on our window sill waiting for my cats he is absolutely obsessed

I have thrown water on him several times and all he does now is when he sees me he runs straight away
Before I started throwing water on him I took him to a vets saying he was a stray, he ended up back at my house
I'm getting sick of this cat I don't know what to do

I don’t think there is much you can do other than cat proof your parameter. Means your cats can’t get out of the garden though.

I had issues with a bully cat - it bit me when I tried to stop it coming into my house!

So I terrified it by getting a wooden spoon & banging it on a saucepan, making a really loud noise.
It never returned,

Some cats don't mind water but they hate really loud noises.