If the fox visits your garden they are best kept in a secure coop and run. He will get them!
It is best if the wire is that strong stuff with small squares as opposed to chicken wire and make sure the run has a roof. If the pen is a fixed one, you should bury the wire a good distance underground to stop him digging under.
Dont forget to lock them in the coop section as soon as they have gone to bed.
Are you in the town? Town foxes are very brave. A big dog fox grabbed my sisters cockerel while she was standing looking out of the kitchen window. She ran out and chased him with the broom. He dropped Elvis and then turned around and came back and picked him up again. Luckily my sisters pretty scary and eventually he dropped him and made his get away. It wasnt long before he was back ... lurking at the top of the garden.

He did visit me once when I lived in the town ..... it was not a pretty site.
I dont like to kill anything ..... but ...... wheres your gun Mr W.