I had a small flock of chickens a few years ago, and never had any problems with our dogs or with predators. Now, though, I have larger dogs and our neighborhood has recently had an increase in skunks/possums/etc. While I would obviously firmly train our dogs to avoid the chickens, install a secure coop to keep them in overnight, and keep an eye on them during the day, it would still be nice to have chickens that could defend themselves a bit if a possum wandered by or if the dogs' instincts kicked in. Are there any breeds that can defend themselves well and would still be friendly to humans and not overly aggressive? Thanks!