If they want to get through.. they will get through. It might make them sick chewing it out, but I think they would do it. Have you considered wood triming with something like liquid nails to help hold it, and nail it to boot. When that liquid nails dries, they'd have to chew the board away.

We have weasels here. They are smaller but just as nasty. The least weasel to be exact. Or some call them a black tip weasel. What ever, they will kill chickens, especially the young ones.

What my friend does is puts a layer of fine wire under the coop and then brings that about two feet extra up the sides and wraps that like a Christmas Present with nice tight corners... It seems to keep them out.

I remember your trouble with mink. Being close to the water as you are, I do not think your troubles are over. Especially with winter setting in and food supplies dwindling..