A Marsh Hawk is a Northern Harrier, that’s what we call them in the South. They do hover like what you described. They have the shape of a falcon but bigger.
Birds of prey can be a pain to identify. Many have different color phases. Google Marsh Hawk grey phase and see if that is it. If you don’t have a bird book you can google birds of prey in Maine, that might work. Regardless, it sounds like you need some bird netting above your run.