Some folks in the BYC buy/sell/trade forum make chicken aprons that cover their backs. The sellers are listed under "everything else for sale." Other chicken folks get pinless peepers for the peckers. It prevents them from seeing straight ahead, so they aim isn't very good - it seems to work very well but, it may have to be on the chicken for quite awhile. Or if they are behaving and it is removed, sometimes the chicken needs a refresher course.
You could do a search "Pinless peepers," to see what they are all about.
and Welcome To BYC! There is a nice article in the Learning Center on Bully behavior in chickens and what you can do to help deal with it https://www.backyardchickens.com/a/bullying-behavior-in-chickens In the winter bored hens are like to starting this, and doing what you can to keep them entertained helps, removing the bully birds for a few days to knock them down in the pecking order sometimes works also. Pinless Peepers will usually put a stop to it if nothing else works. You might try spraying the bare skin of the plucked birds with something like Blu-Kote, that won't stop but it sometimes helps slow down the plucking and might help prevent them picking on sore spots. You might also try upping the protein of their feed a little, that sometimes helps, especially if they are also molting.
