I think there are predators, (owls, hawks, turkey buzzards, mountain lions, foxes, coyotes, snakes and humans too)...everywhere !!!
I would definetly fence them in an area just big enough to run around and if they get startled and you are out with them, they can safely run to the door !!! Mine don't even go out to pee alone, ever !!! And we have a 6 ft wall areound our backyard.. ( a nice wall)....pool,etc... Too many sad stories...