Easy solution. Just park far away from others! I usually find a lonely little space at the far corner of a parking lot, park face-in (the back of most cars is higher than the front) and hike. I will avoid parking next to a Hummer at all costs! Mini-vans (read kids and strollers) are to be avoided as are ladder vans.
I had the same situation with my old 260Z. I had JUST painted it and wanted to show it to some co-workers. So, I parked close and when we went to see it some A-hole had backed into the headlight.
Park far away and get your exercise. You'll get healthy and your car won't suffer!
If you are locked into your parking space as you describe. Get some cheap curb feelers or find a magnet mount CB antenna and stick it in an upward position to use as a noise maker or feeler to get the attention of the Hummers that wish to send you to the paint shop.