Wait at night, with a 22. firearm and shoot them - its probably the best and most humane - if you dont have a firearms cert. I am sure there will be plenty of people in your area who will oblige (and for no cost).
If you cant do that (for whatever reason) try snares - if the fox has a particular path it takes to catch them, snare it up (self explanitory really, and there cheap enough to buy from the local ag merchants). NOTE; Snares have to be checked at least once a day (due to the law) but if you go down to feed the hens it wont be a problem.
Hope this helps!
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