Let me give you a very important tip in regards to "animal urine" in this case. If this is a fox. Urine will NOT serve to deter, and could instead be an attractant. Because of their behavior in marking on things including food, others may come to that smell and search for a stashed food source etc. Urine is very often used by trappers as a "lure" to a set, so do not do this.
If you cannot find it in your heart, understandably so, reach out to your state trapper's association and try and find someone who can dispatch this fox for you. If it is something you plan to do yourself, please by all means learn to tan the fur and put it to good use.
The bitter reality is that trapping can solve this one issue, but it will not prevent further. Unfortunately, free ranging flocks can be plagued by hawks, fox, raccoon, coyote, and roaming dogs as well. We have a large run for our birds for this purpose, to prevent loss. We give them SUPERVISED play time outside in the grass in a moveable little pen. But anyone we have known that free ranges their birds loses some. Even a pen can be entered by a cunning predator - know your local wildlife. How do you prevent a fox from digging into the coop? How do you cover it so a hawk cannot get in? Put a wildlife game camera on the area or nest cam to keep an eye on potential problem animals.
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