I have also had a problem with a fox. We lost three roosters and 9 hens in three different episodes over the summer. Like you, these were chickens with names-birds that we will miss. Most of the chickens were killed while my husband and I were outside, on the property and usually in the middle of the day. I did a lot of reading and spoke to a lot of local hunters about relocating/trapping/killing the fox. I am told that foxes are very intelligent and difficult to kill/trap. Although we live in a rural area, our neighbors are a little too close for us to feel like we can discharge a weapon on our property. I called our county animal control office who referred me to a DNR-licensed, wildlife control service. I was willing to pay the service any amount of money to get rid of what was probably a mother fox with kits. After a lengthy conversation about fox habits, I was advised to purchase coyote urine ($60.00 for 24 oz) and "wick sticks". The coyote urine can be purchased on-line or a pet store may be able to order it for you. Wick Sticks can be purchased at a store that sells hunting supplies. You will have to find the fox den. Apply the urine to the wick sticks (or saturate cotton balls) and hang them or place them near the opening of the den and also near the chicken coop. Continue to keep saturated wick sticks near the fox den until you have evidence that the fox is no longer at the den. Coyotes are a foxes natural enemy and it is very likely that the fox will move on. And no, the urine does not seem to attract coyotes.
Additionally, we built a 1,400 square foot pen a few weeks ago that is as safe as a fortress. We just started letting the chickens out of the pen for a few hours in the evening, but I am definitely leery and uncomfortable when the chickens are out now. I wish that any one of my birds had survived an attack. Good Luck!