Here's some advice, taken from the California Driver Handbook, on how to properly park on a hill. You may want to pass this along to your drivers as a friendly reminder. 

When you park:

• On a sloping driveway, turn the wheels so the car will not roll into the street if the brakes fail.

• Headed downhill, turn your front wheels into the curb or toward the side of the road. Set the parking brake.

• Headed uphill, turn your front wheels away from the curb and let your vehicle roll back a few inches. The back of the front wheel should gently touch the curb. Set the parking brake.

• Headed either uphill or downhill and there is no curb, turn the wheels so the car will roll away from the center of the road if the brakes fail.

• Always set your parking brake and leave the vehicle in gear or the "park" position.