Coyotes, cougar, and bear are possible as we've seen them before. Coyotes are annoying and have gotten a large fowl occasionally when free ranging. Had an opossum kill a hen once. Dogs took care of it. The raccoon that lives out in the woods doesn't come near the house. He's been there years so I'm not worried much about him. Had to trap a weasel once. If a bear decides it wants in, nothing is going to stop it.
It's chainlink or welded wire panels and is fairly secure. Coyotes, hawks, and neighbor dog are only real worries and the chainlink stops the canines. Netting goes over for the hawks, but I pay off the local crows as well with eggs. They chase off the hawks. I keep small chicks secured.
I have the bottom 2 feet hardware cloth covered. If I had more predators, I'd hardware cloth the entire 6 feet. Digging isn't a big issue here except for small predators like the weasel. Too many rocks. I have considered putting cement pavers down in the pens and straw on them. That would stop any burrowing. It's evolved over the years. I keep adding stuff. Tried lots of roof types and the cattle panel roof as worked best for me. It was a LOT of heavy duty zip ties.