So throw a bar of Irish Spring in the boat when you roll it for the winter? Sounds like good incentive to make sure you roll the boat dry.
And if you do get your boat chewed, you'll have your revenge on order Rodentia next time you drive into Lodore after dark...
Nothing in the world is more yielding and gentle than water. Yet it has no equal for conquering the resistant and tough. The flexible can overcome the unbending; the soft can overcome the hard. - Lao Tse