Door UnJam

My house is built on shifting sand and is continually oscillating between Brunswick and Coburg (in Melbourne, Aust) with the direction of travel depending on the weather. This means that my front door frame has a disconcerting habit of moving and getting stuck; really stuck! It's very frustrating to get home and find that I can't get in, because the door has moved and the lock tongue is jammed into the frame. So before I managed to destroy all the screwdrivers/bike levers in the house I design