Can a GPS warn of deviations in the designated path?
Yes most can but that would mean that you would have to keep it turned on all the time. For backcountry on foot, the best use of a GPS is turning it on and off intermittently to establish position fixes and obtain your next bearing. And this is why the new 12 channel receivers are so valuable, because from the time you turn them on to the time they establish a new fix takes mere seconds.
