Make a video of car when receiving it !

We recently rented a car at Hertz Pretoria. On return we were told that there was damage on the car that we will be held responsible for. It was an obscure scratch underneath the rear number plate. Since we know that the car was never left alone outside our premisses this scratch must have been missed on the inspection when we got the car. The staff at Hertz Pretoria was extremely rude. They insisted that it was us that caused the damage and subtracted an amount from our deposit to repair the damage. All of the dents on the pre inspection form was pointed out by us. Although we missed this one obscure mark on the inspection we have no proof that it was there when we got the car. It seems you have to make a video or take photos yourself of the car to protect yourself in future.