[Water Warrior 2]

A Stebel air horn will work well. Had one on the Vstrom and Lynda insisted on one for her M-50. Worked very well the day it saved her from becoming road kill due to a dumb driver. Yeah he was that close when she blasted through his open window with 139 db.
As a side note, air horns will really annoy folks on cell phones too. A woman driver on a cell wandered into my lane and I let her have it. Side by side we were. Scared her so bad she had an unwanted muscle reaction and tossed the cell out the window. Too funny. She likely still hates.