Both clubs I belong to use the "cover the frequency" method. Both clubs fly on land that is easily accessed by anyone. Pins left there for the "remove a pin" method would soon disappear.

In the eight years I've been with one club, and three years with the other, I've never directly witnessed anyone shoot another down, and only heard of it happening twice. Once when the person flying had failed to put up a pin.

I doubt that either method will prevent someone getting shot down, and I seriously doubt that either is superior.
Dennis-