"Not many critters will take chickens during the day unless they're pretty brazen" We got hawks! They'll take up a chicken no problem. I've got a very protective rooster and when I let them free range, I've seen him hide "the girls" under a bush and he stands guard until the danger has passed.
I used to close them up in their coop every night and then let them out into their screened run the next morning, but it got to be a hassle so I did what Mike did. "6" landscape edging buried into the ground all the way around the run. So far so good.