Mustangs that were sold from Rental Companies had the door ding guards. You can purchase them but in my opionion they are ugly and distorts the lines of the car.

 

If you do a search in Google for Door Ding Protection a lot of links will come up. Here is one example;



It has two suction cups that attaches the protector on your door. That way if some looser parks too close and opens his/her door, it will keep it from damaging yours.

 

I purchased the dent repair option from Ford ESP when I bought my 12 GT. Big mistake. Got a nice driver side door ding in a shopping center parking lot within 3 months of buying it. Did the claim and a guy came out and popped the dent (did a good job on that) but only then did I learn it didn't cover paint! My fault for not reading the fine print. That was a $599 add on that I now feel was a waste. I've still got two small bare metal spots on my door, one pencil eraser sized, the other one is slightly smaller.