Maybe you could try waiting until your perennials get a little bigger to give them free range. My flock isn't free ranging at this time, but last summer when they were roaming free they didn't eat my hostas. Rather, they would scratch for bugs under the hostas. Because they were undermining our fruit trees and I want to be able to walk barefoot and not step in chicken poop I decided to stop free ranging the flock. My alternative system is to keep them confined to their pen which is attached to their coop and move them out to a secondary run (movable fencing) during the day in nice weather. I give them our food scraps, weeds and other garden waste in their pen to mimic a free range diet as best I can. So we are still getting nutritious eggs but our landscape plants are not being destroyed. I do miss weeding the garden with Honey my Buff Orpington by my side. She would eat the bugs that I turned up as I pulled weeds. I think I may just bring her into the garden with me next time. I need my fluffy side kick.