Hi I have 2 2yr old barred rock hens and 4, 4 mo old pullets, Brahma, Buff Orpington, Australorp, and Rhode island red, I have a huge pen that I keep gated in the middle to keep the older ones from the younger ones, until i feel th older ones will stop pecking the younger ones, or until the younger ones can stand up for themselves. I let them out in the yard together a couple times a day when i can be out with them to keep them safe from hawks. The 2 B.Rs won't stop chasing the younger ones although they are nearly the same size now. They are already kept separate , so isolating them isn't applicable, unless I create a smaller area and one at a time I put them in chickie jail. What I do now is whichever chicken chases or pecks the younger ones, I run after that chicken, kind of like, see how you like it.. she pretends to just be minding her own business and we watch her inch closer and closer to the younger ones, until she makes a sprint for them and pecks ones tail feathers. Sometimes I pick her up and put her in while the others are allowed to free range, but I really wish I could come up with a way to get them to stop bothering the younger ones. I tell her, if you don't peck the others you can all have twice the space. But they don't listen.. lol... they are not stressed, they have plenty of food, plenty of room. My next approach will be to open the gate and if they start pecking at the younger ones inside the run, then close the gate again and maybe they'll make the connection that they can have the run if they behave.