I don't know how well they'll work on a smooth path, but for MTBing, a bear bell has been recommended to me.

http://kanyonkris.blogspot.com/2008/...gle-bears.html
or
http://www.coghlans.com/images/productBig/481.jpg

This was designed to keep away the furry creatures with an option of being silenced with an attached magnet, but it works with pedestrians too.