Abstract: An anti-fouling protective cover prevents marine growth on inboard/outboard or stern drive marine engines. The cover includes first and second side portions, attached to one another along rear, bottom and front portions. The cover is normally urged open by side-stiffening members and transversely-extending members. The cover is conveniently manoeuvred into place onto a stern drive unit with a standard boat hook, and closed by hook and loop fasteners. The cover is constructed of an opaque flexible material such as bonded polyethylene to reduce the amount of light reaching the engine, thereby inhibiting marine growth.