No! DO NOT SHOOT IT! :evil:
People keep dogs because they will defend the house and garden but no-one is calling for dogs to be rounded up and shot when they get out of their gardens.
Farmers would shoot it and have that right. I'm not sure how a household figures in this - i know my dogs would be risking death if they worried the horses, donkeys and cows behind my house and ensure they can't.. and don't.
IF a dog got out of my garden and attacked a person they'd be held accountable.
If they killed a rabbit you can vouch for the neighbour baying for their blood... I don't agree with your comments that they get away with it.
I think there are ways of getting cats to stay away, but whether it'll work with a cat that has had dinner from your garden, we'll i'm not sure and if it's spraying etc then it's obviously a tom and not been done... they are not as easily deterred when they are like that.
I have dogs, and my dogs keep the cats at bay, we never get a cat in our garden. But getting a dog doesn't mean it'll get on with your chooks either, I have my chooks in a run and covered partly because of the dogs (well one of the dogs - the other wouldn't bother).
Only today I said to my neighbour that her rabbit had better not enter my garden.. it wanders hers and the field behind (so could find a way in - though it'd hav eto really try. My JR would have it for supper i expect and there is no way I'd be listening to her complain if it does get into my garden.
The water gun sounds a viable option.. very much worth a try.. other than that maybe elec netting to teach killer cat a lesson.. i'd be tempted to teach him a lesson on the cat flap side of things too... Grrr