I might give them a little tap on the top of the head with a fingertip, or a "twap" on the chest - a twap being where you brace the tip of your middle finger against your thumb, then release it quickly so it TWAPS against the chick's chest in a snapping motion. The idea is not to hurt or harm, but to commnicate, "this is not okay, don't do that!" This is "speaking" the birds' natural physical language, it is a reprimand like that a parent bird might administer in the moment. It must be swift and immediate, administered at the very moment the naughty bird pecks you. You are saying, "NO! You may NOT peck this hand, this hand has seniority over you! NO PECKING!" I did this with my baby BJG cockerel when he started coming between me and his hatchmates, in his Big Boy stance, and chest-bumping my hand, starting when he was maybe 4 - 5 days old. He would rush my hand as I was trying to clean the plastic tote I was using as a brooder box, he would do this repeatedly and my first thought was, Oh, how cute. My second thought was, This is no beuno! I need him to be a GOOD rooster! So one day we had it out. I determined if he attacked my hand 200 times I would "peck" him back 201 - or in other words, until he backed down. It did not take 200+ times. And after that he was an amazing cockerel, perfect with me and his ladies. Until, sadly, at about 8 months a coyote got him and 4 of my Australorp Hens.
I can chicken-proof the pup as soon as I get a decent enough day to install some electric fencing, but ... not sure what to do about all the neighbors' strays. Can't shoot em, there are cows about. My luck, I'd miss the dogs and hit a cow. Good prime Angus too, and how can I afford that at today's prices? 
