I had a similar problem a couple of years ago. I lost about 20 full grown chickens, including some 10 to 12 lb Black Marans. It started off losing 1 every few days, then escalated. One morning, I heard the crows start screaming, I looked out, and a fox was on top of my rooster. I ran out and shot at him, but I missed. I ended up shooting at him 4 times, never hit him. The attacks ended after one of my boxers chased the fox out of the yard. She ran into a fence, cutting her nose. She missed the fox by inches. I think a bullet whizzing by the fox"s head is a abstraction. A big, fast dog with big teeth is endcoded in the fox"s dna as something to avoid. I"ve seen a fox in my front yard, but haven"t had a fox attack since. The birds killed were missing the heads, and sometimes the heart and liver eaten out. I am north of Howell.
Btw, I came to rely on the crows. When I heard them go nuts, I knew the fox was around. I could listen and track the fox by listening to the crows.