Don't worry. Around here, the land owner usually gets 1/3 of the crop. Harvest chickens when you need them.

I have chickens also and they have a house and a fenced run. However, I let them out almost every day. They love to scratch around, take dust baths, etc. I have 6 acres and they just roam around and so far, have not bothered my garden.
Having said that, I will say that when they are in the pen they will peck at any tiny piece of green they can reach. I know this because I attempted to plant some morning glories, etc. along the fence to shade their run and they just pecked them up !