I planted a row of Nanking cherry bushes on the west side of my run (which is really big) and put chicken wire hoops around them to protect them from the chickens while they get started. As they get established and bigger, I won't care if the chickens eat the lower leaves that they can reach, which will open it up underneath and will give them a cool place to get under on hot days, cover from hawks (my run isn't covered) and a bit of a windbreak. I decided to do this when I observed how much my neighbor's chickens love it under her Nanking cherries when they are out free ranging. I also planted a pear tree in the run, also protected with a 4' chicken wire hoop. Seems to be working nicely and, again, when the tree is bigger, they won't hurt it. But if the run isn't very big, there's almost nothing that they won't eat so you'll need to protect it initially at least.