TRUCK WAS IN PARK WITH THE ENGINE RUNNING. NOBODY WAS IN THE TRUCK WHICH WAS ON A SLIGHT INCLINE. IT WAS STANDING STILL IN THE BACK YARD WHILE I WAS TRYING TO GET THE GARAGE DOOR CLOSED. IT TOOK OFF GOING THROUGH A CHAINLINK FENCE, ACROSS A NEIGHBORS YARD, AND CAME TO REST ON A BANK ON THE OTHER SIDE OF THE NEIGHBORS YARD. THE FENCE AND BRUSH CAUSED SEVERAL HEAVY SCRATCHES TO THE TRUCK.