This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
The ordinary lock can be readily changed so that it will be quite impossible to pick it with a common key.
Ill: The Small End Cut from the Key is fastened on the Pin of the Lock
The way to do this is to cut off the small hollow portion of the key that fits over the pin. This part is placed on the pin of the lock and soldered, or fastened by any other means, so it cannot come out of the lock. This will prevent any ordinary key from entering the keyhole. - Contributed by A. J. Hamilton, Benton, Ark.