After having 16 birds slaughtered by a stoat in under an hour, I've found nothing short 1/4" hardware cloth will keep out a weasel. If you leave one of your fresh dead chickens out as bait, it may come back for you to dispatch as you please, but they're quick little murder monsters. Sometimes a mass of chicken organs, the bloodier the better can tempt them into a live trap, but I personally have never had any luck catching one after Mt father was unable to set them up for me. Never was sure what I was doing differently but I sure wish I had paid closer attention when he was still able.
They can fit through regular chainlink like there's nothing there, you'll have to be pretty diligent until you catch or kill your culprit. Fingers crossed its working alone and doesn't have a horde of adorable little murder babies with it. The one I dealt with came back day and night trying to find a way back in after we fixed our problem area, so best of luck to you and your flock.