for blackfishing in the rocks, I use a grapnel anchor with the line tied on the bottom (upside down) and run a strong zip tie up thru the eye of the anchor and zip tie the line (double wrap on the zip tie). This works great when you need to pull up but the anchor is fast stuck in the rocks. Put enough force on the line and the zip tie breaks allowing the pull of the line to reverse, and pulls the anchor out of the rocks. You do have to pay attention to the condition of the zip tie as they chaff on the rocks. I carry a bag of them and put a new one on before each outing.

This usually allows me to set a scope of less then 2:1 unless it's too rough. Such a low scope can be dangerous and end up swamping the boat. And I'd Never anchor off the stern with this either.

15#'s of Anchor has to be quite a workout?