Not that it did work all the times (I got some green paint on a door once) but I try to park in such a way that the next vehicle's doors wont hit mine. Of course, that works only if I keep the same neighbors for the duration.
Mostly, I try to avoid having the
puddle of oil just above the rear of the car, so I don't have to stand on it if I have to load. And that means all the way either end of the space. I'm not too concerned about having the space look empty: the smart is, after all, rather tall.
Again, the chances of being hit by an inattentive driver are less than by the door of a long coupe, you know, those doors wider than the whole smart is.