Even diving from a boat is no guarantee that you can get by with just full foot fins. My instructor put together a dive trip & the dive boat sank in about 10ft of water about 100yds offshore. Everyone had to swim to shore over a bunch of coral. Everyone from the store had full 3mm wetsuits, booties & open heel fins. The dive masters on the boat only had shorties & full foot fins. When everyone got to shore, everyone from the dive store had rough looking wetsuits & booties, but were fine, the poor dive masters looked like they had been through a meat grinder from going over the coral. Although probably a very isolated event, you never know........