A bell for all passes, and a vintage klaxon horn for the less aware.
The nice thing about the vintage horn is its loud and gets even the most clueless to jump, but unlike yelling which pisses some off, the quaint "ah-ooga" makes gets an embarrassed smile. I sometimes see off leash dogs, but they tend to be smarter and more aware then their owners.
Like with any other issue, we can only control our own actions, and can't change the world. Use the gear and techniques appropriate for the conditions. We expect others to slow down and give us space on the road, we should be willing to slow down and give others space on MUT's.
IMO, a bell should be considered a must have, and there are many small, unobtrusive ones available, there's no excuse to not have one. Bulb horns are cheap, light and effective too, unfortunately, with some cyclists image trumps safety and courtesy, they wouldn't be caught dead with a bell or horn on their bike.