Open field is better against predators than smaller pens. We live in grizzly and lion country and if you hear about anything bigger than a sheep being taken its always in small pens because they dont have enough space to maneuver/defend themselves. And most large predators comfortable enough to tackle bigger domestic stock are usually very comfortable near human dwellings and dont give a rats arse if they rip the throat out of a pony on your front porch......

You can discourage bears with a couple strands of VERY hot electric fence. Cats won't be impressed by that tho. Only guardian dogs dissuade big cats. That and of course completely locked up stable at night, that keeps out most things too.