How secure do you WANT your rockwork?
My answer is 'not secure'. I balance, prop, lay it a bit like decorative brickwork, but what the ancients called 'drystane' or dry-stone, despite it being underwater. This means I rely on natural balance, I make my arches out of post-and-lintel and rely on gravity, and I do everything I can that way.

Why? Why not make it one rigid form that nothing can ever shake?

Because I have had to go in and do a fish-extraction that...