You could also take a GLONASS set with you if you're worried about the military messing about with GPS.
I work with GLONASS nearly every day, we can either use it standalone or in conjunction with GPS. Using both systems together can produce a much more stable fix as the system can always see more satellites. This is not the sort of thing you'd really notice on a yacht though, we're talking about positions accurate to within 10cm post correction which is pretty damn good for a non RTK receiver.
The prudent see danger and seek refuge.