I am will try not to upset anyone's sensibilities, but they will not stop now that they know you have a food source. You will not scare them off either. Fox are also really hard to trap unless they are very accustomed to people. It sounds like these might be so you might be able to get them into a haveahart. Also, they are easier to catch if they are desperately hungry (which yours are not if the neighbor is feeding them). If you do attempt to trap them, you should put the trap along a natural "funnel" or wall that they traverse (it puts them in the path of the trap). Put the trap in place, bait it (raw chicken, cat food, etc are pretty good options), set it, and de-scent the trap with a spray (or one of the natural methods: wood charcoal, dirt/clay, etc). Then cover the entire trap with a black garbage bag and cover that with leaves and/or lawn clippings. Try not to get your scent on things. Some chicken manure/shavings in the area around the trap might attract them too (and cover some of your odor in case it is still on there).
You can also have a nuisance animal trapper come and get them. I am not sure what they charge. Relocation is iffy, you would have to drop it off at least 25 miles away and if you take the fox out of the area (relocation or killing) you might have an increase in population for a time as new fox come in to compete for the newly vacated area and end up with another one anyway (at least it would be one that didn't know you have chickens yet).
They do sell fox deterrent (it is some chemical thing like with the deer deterrents, I think it is the same stuff they use to deter dogs since fox are in the canine family). I have read that ammonia soaked rags are a deterrent as well. I am not sure why, perhaps since ammonia is a precursor of urea they associate it with urine and think some larger predator is marking the territory. I don't know how long these deterrents work.
They probably have a den of kits right now. Cute until they go out hunting with mom and dad and then set up dens of their own around the area... This fox of yours though must be dealt with permanently since it knows where the chickens are.
I just put 6 in my brooder. Have acouple more hatching aswell.
