I'm so sorry to hear about your flock. Perhaps our following info can help..
We had meat chickens years ago. Their run was attached to an older wooded grainery. We figure it was foxes that dug underneath to access the run. The chickens disappeared from the run with no visible struggle. We layed chicken wire around the outside of the run with railroad ties on the edges so they couldn't dig underneath. That worked. But, then something started going over top, so we ran electrified wire around the run. (The run wasn't covered) We still experienced losses. We figure whatever it was climbed the building to access the run and then when we had them shut in, it tore off the opening where the auger used to be put in and gained access to the coop. So we processed them early and gave up chickens.
We got a variety adult chicken mix last year just to have in the yard. They stayed in the large barn at the farm. One of the Silkies went missing one night so we searched and found the dug hole we figured gave access and closed it off. The next night it killed all the Silkies, my black hen and an OEGB rooster. We secured the flock in a large welded wire cage. There was no sign of any bodies just feather strewn around parts of the barn. The next day a Silkie body showed up on the lawn with no head. We had assumed it was coons coming down from the loft but the body puzzled us.
I baited 4 box catch and release traps in the barn. I set and locked them open with wooden dowels. Baited them with large marsh mellows and canned cat food. I did that for about four to five nights and then I took the dowels out. Animals get brave and don't think twice about entering a baited trap. Caught two young foxes in the marsh mellow only traps on two consecutive nights. Our dog killed the last young fox.
I'm guessing you have a wily fox by the way it sounds. I've had excellent success trapping foxes, raccoons and skunks with cat food and marsh mellows. I zip tie a can of cat food (fish flavored) to the bottom of the cage at the back of the cage halfway between the trip door and the back of the cage. I also toss fresh marsh mellows into the back of the cage and out the door.
To fix our mistakes, we plan on using the electrified poultry netting not just as a run but also to enclose the coop within the run as a first defense to keep predators from gaining access to the outside of the coop. The building we're going to be using for a coop is sided with metal. Predators aren't' supposed able to climb the metal walls, from what I've read. We also will use the only 1/2 inch by 1/2 inch hardware cloth after reading about mink/weasel predation on this site. Perhaps this information can help your situation.
I hope you can cam/trap whatever is causing the grief for you! Please keep us posted on your progress. It may be valuable information that the rest of us can learn from. I wish you the best!