Now that he knows where the chickens are he will be back.. Take your rat trap and bait it with the chicken liver. Put that near where you think he is coming into the coop. He might go after that first, but they are blood thirsty little devils and he might not.

I have weasels all the time around here. But since I have no chickens, they are more then welcome to eat the mice. I had one once in my house all winter. I saw him twice. I saw him in the middle of the living room though and so did the dog. The race was on. The coffee tables, end tables, couch all went flying when that Labrador was in hot pursuit. Although that was the last time I saw the white bandit in the house....

When we was kids we used to take chicken liver (they love chicken live and I'd bait the trap with that if I were you) and some gut and hang that on a string about three feet off the ground. Then place the traps under the bait. The weasel jumps in the air to grab the bait, misses and falls down into the trap.

Another way and it is not a nice thing to do.. drill a one inch hole two - three inches into some wood. Trees or a post in the front of the coop. Push some chicken gut into the hole and then sharpen a long finishing nail with a file. You drive that in at a forward angle.. The weasel can get past the nail to get the bait, but when he backs out, that sharp nail catches him right behind the head. He will not let that bait go, and he will end up sticking himself on that nail. Then just go and be sure and touch his rear end with a stick before you pull out the nail. If it wiggles, drive that nail in deeper... If it don't pull the nail and then you can slide the weasel back out of the hole.