Many people, especially those who should know better, are confusing unregulated with uncontrolled airspace. There is no unregulated airspace in the USA but controlled airspace generally begins at 500 ft because ATC radar is unreliable at low altitudes. Generally. The FAA regulates airspace from the ground to 60,000 ft. When anything leaves the ground the flight is governed by FAA rules exclusively. Controlled airspace is that airspace where ATC can provide radar coverage and separation of participating aircraft. That is aircraft on an IFR flight plan and VFR aircraft with a transponder requesting ATC services.
The answer to the question of how much airspace do you own is not answered in the 1946 case U.S. vs. Causby. The decision held only that “A servitude has been imposed upon the land for which respondents are entitled to compensation under the Fifth Amendment”. The case was remanded back to the Court of Claims because “the court’s findings of fact contain no precise description of the nature or duration of the easement taken”.
How much airspace is owned by the landowner and where does “navigable airspace” begin were not decided by Causby. That was not the case before the Supreme Court. The case was simply one of a taking of property in violation of the fifth amendment.
Opinions of the Supreme court are longer explanations by the Justices’ of the reasoning behind a particular action. In the opinion the court said that “The landowner owns at least as much of the space above the ground as the can occupy or use in connection with the land”. One justice’s opinion also used the description of flights as low as 83 ft merely as an example. But these were the rationale behind their decision, and not included in their holdings. 
Navigable airspace is a legally undefined term. In my research I have found a few SCOTUS decisions that reference navigable airspace in their opinions, but none have defined it. Medical Ambulance Helicopters and Firefighting aircraft frequently fly below 500ft. Small UAS aircraft, including personal drones, are advised by the FAA to fly below 400 ft. These aircraft are navigating in the National Airspace System, so that would make airspace below 500 ft navigable airspace even though it is in uncontrolled airspace.
An overflight of 100 ft or even 50 ft over your typical home is probably not trespass. If a drone stops to watch a teenage girl sunbathing nude in the backyard, then the drone operator is likely violating trespass laws regardless of the altitude. We don’t need a definition of how much airspace does the homeowner own because there are already plenty of state and local laws that cover trespass – we don’t need any more rules. These laws are technology agnostic, meaning that it doesn’t matter if you’re using a drone, a kite or a camera on a pole. Trespass is trespass.
There is a nude sunbather in this Photo.
Shooting down a drone would likely violate weapon discharge ordinances and would also be a violation of 18 U.S. Code § 32 – ‘Destruction of aircraft or aircraft facilities’. Shooting at a drone 200ft altitude is not protecting anything. Period.
Unless the drone shoots first.