All anchors have limits. I've experienced that my Rocna 20Kg might drag in soft mud if I back down at full reverse in 20k of wind (59HP engine and 19" diameter prop). I haven't dragged in Tashmoo but also haven't been in 60+ knots there.

The other thing that's challenged my Rocna was cobblestones (in Orient Harbor NY). I suspect you'd need a very heavy Fisherman anchor there, or just skip the anchor and set massive engine block (kidding). In sand the Rocna is immovable. Regardless, it's a very good anchor.