Predator proofing is the biggest concern with quail, as everything will eat quail. I have hardware cloth rabbit hutches for my quail because I didn’t have the space to make them a big predator-proofed ground pen, but if you can sufficiently protect the boundary of the pen with hardware cloth they can be on open ground. Your pen will need a top though as quail can fly away and birds will take them!Would a fence be enough to deter predators? I'm afraid of the fact most of their needs might lie with predators, although less needy birds are definitely a pro for me!