I know the legal limit we are supposed to go is 400 feet, but what do you do about hills? I live on the top of a large hill about 150 feet high, and there's a vertical drop off on the entire northern side of my property that drops down 150 feet to the level of the rest of the area. If there are planes flying around the area, I'm assuming the altimiter of their plane shows the height from the rest of the area. They might be flying at an altitude of 500 feet a half mile away, but when they come over my hill, they might only be 350 feet above my yard. What do I do?