Thornless blackberry is a great idea!We had lots of grape vines in our yard and the chickens never messed with them except to hang out under them in the shade looking for bugs. They also liked our thornless blackberry for the same reason although I’m sure they ate some berries. I planted a boysenberry and several honey suckle around our coop. A big blackberry bush can provide shade and enrichment but it takes a few years to get to that point. Honeysuckle grows quickly but it doesn’t provide a lot of shade. I planted herbs in a pot outside the coop and I also put things inside the run to block the chickens from pecking at any part of the vining plants while they were young. Hope that helps