We just saw a weasel run through the yard early this morning, with a mouse-size creature in it's mouth. The coop is fairly secure, but I think maybe I should avoid letting the chickens roam around today.
Last year we lost 7 hens to a mink, before we were able to trap it. The mink was coming up through a rat hole in the dirt floor. The dirt floor has since been lined with hardware cloth and we had no rat problems last winter.
The nearby compost and garden area is another story, - full of rodent holes. The weasel may have lived here for years and we just didn't know, but seeing it out there makes me nervous.
Your experience is why in days past, when chickens were on most farms and on a lot of urban back lots, the A#1 floor of choice was always cement. It offered a ton of benefits over dirt, and stopping rats and a whole host of digging predators was at the top of the list. It allows so much greater security. To anyone contemplating more or less permanent chickens on a large enough scale to warrant it, a cement floor should be considered. And doubly so if you live in an area or neighborhood infested with rats.
BTW, weasels, minks, etc. are not the only predators attracted by these vermin. Skunks, fox, coyotes, snakes, hawks and owls also prey heavily on them. All of them also like the taste of chicken, which is often a big, easy meal for a hungry predator.