MissChessy, we had the same problem, and made a very simple fence with metal posts and 40-inch chicken wire around our large garden. It worked great! Over winter, we allow the chickens in the garden to dig everything up and help compost the mulch, but this week we just put the fence back, and they don't think to fly over it. I don't know why -- except maybe they're lazy fliers. they also have lots of other interesting places to roam around the barn buildings and yard and fields, etc. Maybe once a month a chicken finds a way into the garden, but we just find the hole and patch it up.
You can also buy simple chicken fencing from Premiere that is electrified. It is an easy movable netting that can be solar powered. I didn't get it because it was more expensive, but my friends us it.
Good luck!