Do they have dogs? If so, simply the smell of the dogs might keep the foxes at bay. We have a lot of foxes around where I live (out in the country with no neighbours for miles, so plenty of territory for foxes). Along with our three dogs, we currently have two chickens (more due to arrive in a few weeks). They roam free from about midday onwards (after I've collected any eggs) and take themselves to bed just before sundown. I shut them in at some point later on. The only time they are shut into their compound is during hunting season. In the five years we've kept chickens, we haven't lost one to foxes. The chickens have proved surprisingly confident with the dogs, will take one on if they think it's being a bit too pushy and will defend each other.
My only doubt about your friend's plan is the timing of his automatic door. He'll need to vary it as the days get longer and shorter to ensure his chickens aren't left outside on a long evening once the door has shut. Like joyfull, we don't clip our hens' wings and I would recommend your friend do the same.
Also, ours never had a 'traditional' mother hen. While ours have probably never seen a fox, they have seen other predators, as we also have eagles and buzzards here too, and they know instinctively what to do. When they hear one or spot one in the sky, they stand absolutely stock still and look at the ground, presumably to avoid their eyes giving them away. They coo quietly to each other as warning calls and even our dogs and cats are now alert to their behaviour as a signal that trouble may be afoot.
I'm sorry if others disapprove of this approach. Our chickens' mood noticeably improves when they start to roam about the place.
If your friend is keen on "free-range" birds, he might like to consider guinea fowl as well. They kick up a right racket at the sight of predators, apparently, and would alert to the presence of foxes.