Bio-fouling is the unwanted adhesion of biological materials to any wetted surface and it grows continuously in thickness with sustained immersion. Fouling causes severe structural loading on all the submerged components of marine electricity generators, lowers the efficiency of generation and can disable a generator totally through the clogging up of moving components in turbines or pumps. Existing anti-fouling coating techniques applied to ship hulls cost £3.8 billion pa worldwide, yet fouling still causes an extra fuel cost of £5.1 billion pa. So for marine generators a novel fouling prevention system is proposed, usable on any generator design, which deploys low power quasi-continuous low KHz guided ultrasonic waves, mode selected both to repel bio-molecules and couple into all the submerged generator components from a single source location, to cost effectively, without harm to marine life, prevent fouling with 100% surface coverage, avoiding all downtime for fouling removal.