Aquanaut10, Get a cheap pair of full heel fins for trips to warmer climates. I use Sherwood Shoreline full heel fins. Purchased them for about $30. They are lightweight, easy to put on (out of the water and in the water). They are no harder to put on than open heel fins. Mine go on like slippers. I have never kick out of them and I have pushed full force with them although I think if you are going that fast you are missing all the great stuff. Slow down and enjoy the ride.
If you want extra warmth, I use a neoprene sock. Its enough to add warmth but does not compress enough to make any difference at depth. It also provide grip for those shore dives where you have to walk across slippery rocks. They wouldn't help for a sea urchin, but neither would my boots if the spine hit the side. Easier to just to take small steps and look where you are walking.
If the boat requires you to remove fins before you climb the ladder, its actually quite easy. Just remove them and stick your thumb in the heel. Makes it easy to climb the ladder and you will not loose your fins.