For cover for chickens, Hazel nut shrubs will grow 15' in one season once established. They have multiple trunks about an inch in diameter and grow quite wide too so provide nice cover. Easy to shape too. The shrub can be used as firewood as it grows so fast and has lovely catkins in Spring that birds love. Blue elderberry can reach 20' in three years.
My girls did not bother my new shrubs and I did not protect them. But I only have three. The girls do love areas of my yard with cover, a blessing as we have hawks here. We have also lots of Mediterranean bay which is an evergreen shrub. Smells lovely and can be used in cooking. Just planted high bush cranberry, Douglas spirea, twinberry, Indian plum and rhododendron.
I may leave a tree in my yard which appears to be dying. The woodpeckers and cedar waxwings love it. Apparently Audubon suggests having some snags. I know not everyone likes wild birds but woodpeckers are not a threat to my chickens. Will see if I can stand looking at it. Every time I decide to cut it down, Ibe seen some wonderful birds in it. I may plant something under it so if I do remove it the area won't be so bare.