One of the most important components in the mitigation of corrosion is the proper type and application of protective metal coatings. Proper coating effectively insulates metal from the electrolyte surrounding it, again eliminating one of the components necessary to complete the galvanic cell. On a drive unit on which this coating is beginning to be compromised, this puts a higher demand on the anodes, and once they're depleted, the drive begins to corrode rapidly.
The best base coatings we have available to us today are any of the epoxy barrier coats available, such as Interlux Interprotect. Apply this to all underwater metals, including bronze through-hulls, before any anti-fouling coating goes on. On drives that have already been submerged in salt water, another hidden enemy lurks: soluble salts, which are invisible and tasteless. These microscopic particles cause premature paint-system failure and must be cleaned away before any epoxy or paint is applied. The trouble is, these particles are difficult to clean off. In fact, a typical boatyard pressure washer won't remove them. Yanmar, for example, recommends both a test kit and a biodegradable neutralizing wash made by Chlor-rid Corporation (www.chlor-rid.com). If you're recoating a saildrive, this step is super important to ensure that the coating stays on the aluminum.