(Hey, my first Travis McGee post! Love the books!) Excellent point, Matt. We have so much access to technology these days that we can easily forget that there are other ways of doing things. I believe that the military is currently able to instantly shut off certain regions and even encrypt the entire GPS system so the concern is certainly valid. If for some reason the GPS navigation isn't working in the future, a "stash" could still be recovered old-school using compass and tape. Assuming that laser range finders, internet satellite maps, and digital compasses are still functional, recovery would still be a snap.
I would use GPS, for sure, but only while considering that it’s a convenience, not a permanent feature. The old school method of using landmarks, azimuths, pacing etc should still be used along with GPS, and most importantly of all, one must use fixed objects such as giant boulders as references. Even big trees could be gone when it’s time to dig up the goods. Or a shopping mall could have been built across that fallow field. National Parks and other places that will (probably) never be built on are recommended.