Each one of these could be a potential missile used against us.
edit: ( I think the real concern in this situation would be reverse engineering with an eye to finding vulnerabilities to be exploited in other drones, not so much reprogramming the one and only they have )
Is it possible to somehow sign GPS coordinates? (Perhaps sync an internal clock at each mission's start, and check a time-based signature?)
If not, are there practical challenges to integrating the output of a drone's engine and calculating the path travelled, instead of naively believing satellite coordinates?
Actually, wind must make that difficult. For a car, you can attach a magnet to each wheel and count the surges as it passes a sensor on each rotation, to give you an idea of where you are. Due to the external forces on a drone, you would probably want to measure forces with an accelerometer/gyroscope, not engine output.)
What are the challenges involved in such? Is internal-location tracking even feasible?
GPS spoofing/jamming only works for systems that use GPS navigation systems; military weapons and systems have never used GPS navigation. Inertial navigation systems are spoof-proof.