got a couple road cones? you could cordon off your bike ... or maybe some yellow caution tape? wrap the bike in it...
if you have a mig welder handy you could tack a couple rusty nails onto the outer edge of the mirrors...
take up 2 spots park across them ....
paved parking lot??? if so maybe make a nice smoke show with a big doughnut around your parking spot....
stop greasing your mirrors and start geasing theres!
alot of trash laying around your bike will make them stay away also... I hate the idea but hey everyone will walk around trash instead of picking it up.. LOL