We did back mounted doubles. My instructor cave dives on back mounted doubles and knows that I already practice self-reliant concepts, so he wanted to bring something new that I could learn. So rather than using a pony bottle, which I've got plenty of experience with, we mixed it up. This made the training far more interesting since I got to experience new gear configuration, a different concept of redundancy, and valve drills. He knows I do a lot of DPV diving since he's one of my dive buddies on the private boat I do most of my diving from, he suggested we mix in using our DPV's on day 2 to simulate how I most often dive. It was a lot of fun and I really enjoyed doing and learning something new.
