More than bad parking I think the dents usually come from people parking nicely then carelessly opening their doors too far...

Indeed, once I was wating in the car in a supermarket car park when a 4x4 pulled up next to our Citroen C5, the guy inside opened the door so hard in to the side of our car it rocked.
If that wasn't bad enough less than 2 mins later another 4x4 pulled up at the other side and did the exact same, this time a woman, its amazing how little consideration these people have for other folks cars.
I wouldn't suggest practicing parking in a place full of parked cars either, at least bashing your garage is only damaging your stuff rather than other people's cars, that could cause utter chaos!

The idea with the cones is a good one, depends on if the police turn up and ask why your are parking in a cone garage in a public car park and where the cones were "borrowed" from though!
The rozzers have it in for motorists now it seems.
