This happened to mine from not using a proper tool to remove them from the door.
In any case, from now on I will reinforce every door panel I ever use, even if it's brand new.
If your door cards are in good condition, you can just use some thin super glue (get the model plane stuff) around the holes for the clips. It will soak in to the door card and go very hard making them much stronger.
If you've had some of the clips pull out, or the card has been damaged, you will probably have to use fibreglass.
I just finished my second door card. The first one went back on a treat and is a buttload (metric, not imperial) stronger.
I used fibreglass mat for the ones that were damaged, and just coated the good ones with the resin to give them more strength.
![Image](https://s20.postimg.cc/7f70jky99/IMG_20170107_165008.jpg)
![Image](https://s20.postimg.cc/uutj2o7e5/IMG_20170107_165021.jpg)