our first hens (about 30) were completely free range for ages, mainly in farmyard, and didnt lose any, until the night i 4got to shut them in, when they were all killed.
now i made a big run for them with 6 ft high fencing and not lost one (except to a cat). the other hens in a different area have a run with pop hole to a paddock, which they cross to explore the woods, of these we lost 9 in one week.
i think it depends how much u are out and about, near where they roam. busy farm yard with dogs milling around would keep the fox back i would think.