Well, I didn't lose any hens but, I almost did. I had a very well protected coop, we had double welded wire run, a rock trench and a very strong coop. Well, unknown to us a rat must've chewed a quarter size hole in the corner of the coop and an Ermine got in. I went out to shut up my chickens for the night and I heard them cackling loudly. I went out and I thought it was a ferret because, I'd never seen an ermine before. I chased it out of the coop and went over to the neighbors asking if they had a lose ferret. No, they didn't I went back into the coop and the ermine was back and it was attached to one of my GL Wyandotte hens. I pulled it off with my bare hands and I had to kill it since it kept coming back.
We promptly lined the flooring of the coop with 1/4 wire hardware cloth and stuffed any holes with steel wool and hardware cloth.
I also put a 500' range baby monitor out in the coop so I could keep an ear out in the coop, so if the chickens started cackling I could go out and make sure there wasn't a predator.
So far no loses.