There is a common misconception that you can overprotect your drive by using too many zinc or sacrificial aluminum anodes. This is not true. The corrosion potential of any metal is a voltage that can be measured by a reference electrode. Such measurements in water commonly are made with a silver/silver chloride reference electrode. The corrosion potential of a sacrificial anode is a characteristic value for that metal, and it does matter if you have one piece of the metal or 100 pieces. The corrosion potential stays the same. Of course, 100 anodes would be expensive, heavy, and a considerable drag under water. Only by increasing the corrosion potential by using a different anode material (such as magnesium in seawater) can you overprotect your drive.