I've always liked the Polk Marine series of speakers, though keep in mind that none of the speakers, Polk or otherwise, will be truly "waterproof". They're all water resistant at best, only designed to handle the occasional spritz of water as would be seen on the deck of a boat when swimmers climb aboard, or the family Fido shakes himself dry.
No speaker is intended to be hosed down, or dunked, like we might see in an off road environment.