We have the pecking problem, too. It started with the chick who turned rooster and was rehomed. After that, one of the barred rocks started and now everyone is pecked, and several have naked butts. They have more than the minimum recommendation for space per bird, have toys and treats, I've upped their protein, etc., but no luck. I bought an apron, and have that on one of the hens as a trial, and we will be using pinless peepers, starting today. I think there are flocks where this just is a problem, and flocks where everyone gets along. Probably very difficult, if not impossible, to predict. The methods of introduction mentioned here are good ones, but just didn't prevent trouble with my particular flock of birds. The worst picker is a beautiful pullet who lays a pretty pink/peach egg nearly every day, so I would hate to rehome her (and I think she would start her bad behavior elsewhere, anyway).