Where is it getting into your chicken coop?
A 220 conibear at that opening will catch and kill it, but beware if you have cats or dogs of your own, it will kill them as well... Next best, is a #1.5 leg hold. You will have to de scent it, settle it into the ground and cover it, making the cover look natural, without leaving anything that will hinder the trap.
Fox are nervous and sly. If the trap smells like metal, or you, it will not catch the fox. We used to boil our traps in walnut hulls and hang them out to weather. When set, we used fox urine to cover any scent left behind. Set the trap where the fox has to walk, preferably where it might jump, or land to access the coop.....