Since I began diving over 27 years ago with advanced, cave, etc. certifications, I have been lost at sea once and I have found a guy floating out at sea that was lost once as well. Dive boats out of West Palm Beach, fl. Were bad for awhile losing divers but I think it has improved somewhat over time. I will not go diving on a boat anymore without a PLB since I almost bit it when I was lost at sea from a dive boat. I was fortunate to be seen with a dive alert and a big dive sausage and a lot of prayers while floating out in the big ocean. You cannot depend on nobody but yourself if things go astray. And this goes especially true when you’re in a cave and you are on a short time clock. I like the VHF idea to yell at the boat as well as well as the PLB. The PLB when in the ocean may be awhile till you get rescued while you are keeping the sharks company, but the VHF will help as well if there are nearby boats that may aid you in getting out of the water faster. Both would be nice, and there are a lot of underwater containers to put them in which doesn’t consume much space. OMS, watershed, McMurdo, DUI to name a few.