I have retrieved lots of anchors scuba diving in Lake Mead and the Colorado
river. Some were easy, some stuck fast. I would suggest matching the
anchor to the terrain as the major factor. After that, it's just dumb luck.
I could see just how some people lost theirs, tracing their remnant of
anchor ropes. It was amazing that most of them just had to back up, but
probably didn't have, couldn't read, or couldn't see their compasses. A
couple took prybars, but most just came out when pulled in the right
direction. Lots of them had that slider ring.

Steve