This issue comes up here from time to time and I deal with it multiple times each year. Some free-range hens have a propensity for nesting away from nests providing which can mean the location is in a highly vulnerable and exposed location. With the aid of dogs I can usually locate such hens early in the incubation cycle and take steps to compensate for the exposed locations. The most frequent approach is to simply drop a pen over such a hen that obstructs predators from simply walking up on such a hen. The pen is placed so hen is directly in center so something like a raccoon can not simply reach through. At night the pen is kept down while during the day the pen is elevated so hen can come out when she needs to. Feed provided is done some distance away so smell does not attract predators. I also like to place a rug on top of pen to block direct sun during hottest part of the day.