It's always a risk to let our flocks free range. Not only foxes but hawks and any number of other predators will be looking at them as a potential meal.. even more so in winter when the preds natural prey is hiding out till spring. We have to make the decision do we keep them inside a fence or let them roam around unprotected? I have half acre fenced for my flock but alot of days when I am home and about outside they can go out of the fence and forage if they want too. When I am not home they are inside the fence. In winter they are not allowed out of their half acre since with the windows closed i cannot hear what is going on, Just today my rooster began screeching not his normal sound so I went out to see what was going on, a huge red tail was sitting in a tree right above their area, All the chickens had went for cover, my Muscovy's? were all sitting out in the open [under leafless trees looking up.] I don't think Muscovy's would be able to escape a sly fox. If one was to get away he would just go after another. So again most of us who choose to let our flocks free range take a risk of losing some or all we have had members come in to say they were completely wiped out because they didn't want to lock their Scovy's up at night. thankfully in the over 11 yrs I have had Muscovy's I haven't lost any to a predator. Mine are locked up at night too. There are many kinds of predators and one of the worse is free roaming dogs. Not just wild animals.