I suggest looking into live stock guarding breeds. Surely someone has experience with smaller dog breeds that can serve purpose of wooping fox but not cost too much to feed and house. We had black and tans raised as puppies in keep with chickens that kept varmints out. Since you do not have a dog now it opens up option to get pup that can be properly imprinted on birds. One acre is a small area for a dog to patrol therefore some sort of cofinement such invisble fencing might be needed.