Had this conversation with my local pool's lifeguard this morning while i was scoping out my "extremely" local pool (not even a 5 min walk) they allow fins if it is super quiet, they allow pretty much anything if you book the lane, and they have a swim rescue class that predominantly uses monofins in their exercises. So i'm looking into that. I would love to book a lane but feel it would be better with a small group of mers rather than just a me...