On May 29, 2004, at 1005 Pacific daylight time, a Cessna 172M, N5440H, impacted a fence post after departing the end of a turf/grass runway during a simulated forced landing at Vernonia Municipal Airport, Vernonia, Oregon. The certified flight instructor and his student were not injured, but the aircraft, which is owned and operated by Twin Oaks Airpark, sustained substantial damage. The 14 CFR Part 91 instructional flight, which departed Starks Twin Oaks Airpark one hour earlier, was being operated in visual meteorological conditions. No flight plan had been filed. There was no report of an ELT activation. According to the instructor pilot, who failed to submit a NTSB Form 6120.1/2, he was performing a simulated engine out forced landing as a demonstration for his student. As he neared the approach end of the 2,940 foot grass strip, the aircraft's airspeed was faster than he desired, and during the flare, it began to float further down the runway than where he had planned to touch down. He said that because of the excess airspeed, he was unable to get the aircraft to touch down until approximately 1,000 feet down the runway. After touchdown, he attempted to stop the aircraft before it reached the end of the runway, but since he had landed on the wet grass, he was unable to get it stopped before the aircraft went off the far end. After departing the runway, the aircraft collided with a nearby fence post.