The area in which I live sees not only foxes but badgers, pine martens and birds of prey all of which are a threat to the hens. To reduce the risk of attack, I have installed an electric fence which every now and then I check its’ strength (with gritted teeth and much reluctance)…that’s if one of the neighbours dogs hasn’t kindly already done that for me!
Spring tends to be the foxes most active time of year as they’re having to feed their young so it’s best to be extra aware during this period. Locking the hens away at night improves their chances against a fox attack. You must also ensure that your coop is strong and durable. I’ve heard foxes can break into wooden coops although these must be the most determined of the lot!