Install an air horn on your vehicle - it's a great attention getter (sounds like one of those big dump trucks) and it helps to remind people that the lane they're drifting into is already occupied.

The horn on my vehicle is exceptionally good - much better than those girly man peep peeps that Landbruisers have :-). I use the horn to ensure my safety and not gratuitously like the bozos who start in as soon as a traffic signal turns green - goodness, how fast do you expect me to take the foot off the brake and on the gas pedal?

Signature line > "You can't fix stupid"