@PalmerLakeAnon
I LOVE your idea that McSherry was the one who got disoriented and not Dametz. Actually, both of them could have been. Unlike hiking where you're constantly taking a bearing on your whereabouts and looking at your surroundings, with rock hounding, you're looking at the ground. You could easily lose track of where you are.
The two rock-hounds may also have lost track of time.
I would guess Dametz wandered off a bit. At 81, his voice would have become thin, and he may have had difficulty shouting. I believe it's easy for dogs to not get a scent: we had this happen in the Paul Miller case in Joshua Tree. Air may have been moving up and down those gullies as the day wore on; that may affect scent, too?
IMO it's likely he'll never be found, unless maybe there's a fire in the area that denudes the landscape. I suppose someone could go into the potential areas with a metal detector to try and get a ping on the tools?