content: Incorrect. It absolutely is the low pressure zone trailing the rock that keeps the gopro sinking at the same rate as the rock. In fact, the energy to pull the buoyant gopro down must come from the rock itself in the form of gravitational potential borrowed by resisting the higher pressure zone above the gopro which is ultimately what drives it down. Any second or third year engineering student could tell you this without needing to perform the experiment. The Mythbusters get stuff wrong all of the time.