I could never kill a fox. I really don't like them, they've had enough of my animals over the time, but I couldn't kill one. It's difficult because we have cats and obviously they like to come and go (we have a cat flap). I'm sure I've heard that men's pee or dog poo can help deter them. No idea how true that is.
We had a fox do a "stealth attack" on one of our previous chickens actaully. Well, we were indoors, but the back door was open and we heard a load of squawking. Luckily we got there just in time, although I thought our chicken was dead as she was all cowered down, perhaps playing dead (if they do that), although that chicken was never the same after that.
They just drive me nuts. I wondered if leaving a radio on in the garden while I'm inside might deter them? Our chicken is older now, so I don't really want to spend a fortune.