Better yet, go get scuba certified. 10ft, you'll get a long time on a 80cf tank once you get used to it. Oh yea, noticed you said you can hold your breath a long time.... don't, ever on any kind of scuba. You're breathing compressed air, at depth. As you come shallower, that air expands in your lungs. If that air has no place to go, it will make it's own place to go - ie, the chest cavity by popping a lung. You really don't want that to happen. You can do that in as little as a 4ft depth change. Also, ditch the rocks and pickup a cheap dive weight belt. Put it on with a right hand release. Much faster, and easier to drop that should your air source fail than try to dump all the rocks. Sorry if this comes across as lecturing you, but I've seen far too many people die underwater since being certified as a divemaster back in 2001. Every death I've seen has been preventable. Every single one of them. Ranging from really stupid things like not checking your pressure and running out of air, to sneaking into a night dive without a buddy, to an instructor ending up dead, in a shallow pool on a rebreather because he had no training, or clue how to use it.