Keeping the shark near the surface so that it cannot dive under the submerged lift is one of the tricks that had to be worked out on the fly. McBride came up with the idea of having the balls slide on carabiner clips and using a butter knife taped on the line to keep the ball up close and personal to the shark so that the shark cannot dive. While a lot of neat innovations were cobbled together for the overall mission, this trick might have been the one that allowed it to work.