We could just keep them in their fox-proof coop all day, but that/s not very good for the chickens
This is false. They would not be killed (a positive), and they would be in a familiar environment - which chicken love. They love the familiar. They are prey animals, and are hardwired to avoid predation, and the familiar provides them with what they are hardwired to want.
Of course, they do love scratching grass and eating bugs. While a chickens cannot smile, they sure look happy when digging a dust bath, finding a juicy bug or exploring the compost pile.
While you have foxes, and an abundance of them, you are going to have to change up a few things. Besides keeping them locked up, you may want to use an electric fence with a good amount of juice to really zap the canines after your chickens. If no electric, then get solar and make sure it’s good and charged for their evening excursion. Really, an electric solution is a really impactful solution to each animal that experiences it. Then they teach their young to avoid it too.
You can go the route we did: make a predator proof run. It’s taken a few years to get there, and we have more issues with raccoons than foxes. But, we have just one more thing to do to completely predator proof it. However, it’s time consuming to do that and more $$. We do let our out to explore when we are nearby, and we do not have woods that are very close, so that can help minimize some predation.
Premier one electric fencing is highly recommended by many BYCers. I’ve looked at their options in the past and they have pretty much any solution you might need at various price points.
Good luck!