We've had good luck in the open ocean with Dietzman Death Squares:
Blue Water Shark - from 1992: Last month I was diving as pivot diver on a blue-water night dive off Bermuda. There were two collecting scientists and a National Geographic cinematographer with me on the dive. About 25 minutes into the dive I saw a large shark (probobly C. longimanus). It came toward me and I pushed it away with my light. I pulled on the tethers to signal the other divers and the shark went toward the photographer. He saw it and, of course, began filming. The other two divers followed the plan for such incidents. They detached their tethers, came in to me and then released their tethers. I dropped my tether and signaled them to surface. The three of us ascended, facing outward, at a normal rate. I watched the shark and photographer. The shark turned toward us and circled around us near the surface. I dropped a Dietzman Death Square that I carried for such occasions, the shark followed it as it sank. I told the two divers to enter the zodiac. As they clambered into the boat the shark came right back up, but stopped at the photographer, who, of course, began filming again. I dove back down to the photographer. When I got to him the shark had gone back toward the surface and was directly above us. I dropped the photographer's tether, we ascended back to back, the shark swam off about 20 feet and was just at the limit of my light. I waited until the camera was in the boat and the photographer was starting to climb aboard. I dropped another Death Square and as the shark dove after it, I quickly followed him aboard.
Greg Dietzman, a tech at WHOI got the idea that sharks would follow little squares (maybe 3x3 inches) of galvanized sheet metal, and it worked, at least long enough for us to get back in the boat. They became know as "Dietzman Death Squares."
