Preparing to park into a parking space in an off street parking lot the vehicle forcefully and rapidly accelerated on its' own and crashed into a fence. I was not accelerating. I attempted to stop the car using the brakes but they did not engage quickly enough to stop the rapid, forceful, and without warning acceleration. Buick has been contacted about the defect. Buick ran extensive diagnostics on the car and denies there is a defect. Police came to the scene and advised that given the 2 other incidents that I have experienced, the car is unsafe to drive given potential damage to others. A police report was filed.