GPS Error
As a surveyor, I would always make a site plan of any location that I planned
to return to: even if I was locating myself with GPS. This need only be a
sketch with major features: maybe for you, 3 rough compass bearings to
prominent outcrops would be enough for you to say " my GPS antenna was about
here". Presumably you'd then have more accurate measurements from your GPS
antenna position to the actual work site.
Rob