Halt clamp:
http://www.nashbar.com/profile.cfm?c...reid=&pagename=
A can of Halt doesn't weigh much and has saved my legs from being chewed on.
Nashbar doesn't have a picture of it, but this link is for a plastic clamp that holds a can of Halt! to your handlebars. You can grab it and spray in seconds. Just watch for the wind blowing it back in your face.
Halt:
http://www.nashbar.com/profile.cfm?c...eid=&pagename=