| Discs are great for driving and the standard concept has not changed in years. However, we are talking about parking. The drums held better for parking. You can go to other forums and find where cars have released after being parked for a few minuets even with the brake fully applied. It happens if the conditions are right and sadly the only thing that will stop it is by putting the car in gear. Turning your wheels can also help as you will hit the curb (if there is one) if your transmission fails to hold the car.
Bottom line is that you should never park the car without leaving it in gear.... | 
