That is the one thing that, as of right now, we don't have. However, we do have a satellite phone, regular cell phones, GPSs (with the back up map/compasses), and FRS/GMRS radios. We also plan out the routes we're taking each day and leave it with family (with an approximate return time of course and we check-in along the way).

Hopefully that, combined with the survival gear we carry and our training, will be enough to keep us alive and rescued if the need arises. But, I'm definitely thinking of picking up a PLB or two and teaching my father about them. It seems like it's by far the best way to ensure rescue.