If you only have a few hens picking greens for them is great. I have 20 adults & 12 chicks so picking for them would be a bit time consuming. Hope you haven't sprayed any herbicides or pesticides on your lawn prior to collecting greens, It may end up in the eggs and meat if you eat them.
A while back I was letting my hens free range, until the head count started dropping. The culprit turned out to be a pair of Golden Eagles. Well they are an endangered species so I couldn't do much about it. My choices were feed the Eagles or pen up my hens. I chose the latter. It wasn't long...