Or hang rubber bumpers on the side, as they do with ships, tugboats, etc. Might look funny.

many cars already have a strip of plastic on the side pannels and doors to protect the paint from doors, but some new models lack this for more aesthetic smooth sides, or have this strip painted same as the rest, so that the strip can be chipped and look as bad as if the door had hit any other area, the current system just needs to be improved. and people should realize that by having this common feature, they may be giving up some of the aesthetics of their new car, but in the future that plastic strip will look a lot better than a million little dings.