The pilot stated that he and his pilot rated passenger were in the pattern doing touch-and-go landings when he decided to demonstrate the procedures for a return to airport simulating a loss of engine power after takeoff (downwind landing). At 400 feet the pilot reduced power to idle and executed a 45-degree right turn back towards the runway. The airplane touched down on the main gear about halfway down the runway and immediately swerved to the left. The pilot applied full right brake and rudder control. The left wheel exited the runway on the north side. The pilot was able to maneuver the airplane back onto the runway and realized that the airplane was heading towards the drainage ditch off the end of the runway. With about 1,000 feet of runway left he applied full power and set best climb attitude, but the airplane was not able to clear the fence at the airport perimeter resulting in substantial damage to the fuselage and wings. The pilot reported no preimpact mechanical malfunctions or failures with the airplane or engine that would have precluded normal operation.