The jump would be nothing to a fox. Time will tell on your hen. You can dig a trench around the complete perimeter of the coop. fasten hardware cloth around the bottom of the coop and a good foot into the ground and bury it. It is actually effective to have the hardware cloth come out at an angle about that far. It doesn't have to be buried if it lays on the ground horizontally from the base of the structure. Make sure it is fastened securely to the coop.