The pilot was practicing full-stop landings in the tailwheel-equipped airplane while on a local personal flight. The pilot reported that his first two landings were uneventful and that the surface wind was calm. He stated that before his third landing he had made two go-arounds because the airplane was not established on a proper descent path to the runway. The pilot reported that on his third attempt the airplane touched down with excessive speed and about 100 ft before the halfway point of the 2,000 ft long runway. The pilot applied "moderate" braking about 600 ft from the end of the runway in attempt to slow the airplane, but the airplane began to slide on the dew-covered grass. When it became apparent that the airplane would not stop before the end of the runway, the pilot intentionally ground-looped the airplane in attempt to avoid a runway excursion. However, the airplane continued to slide off the end of the runway and the lower right wing impacted the airport perimeter fence. The airplane then nosed over onto the fence. The lower right wing main spar fractured during the accident. The pilot reported no mechanical malfunctions or failures with the airplane. Postaccident examination confirmed flight control continuity and found no issues with the wheel brakes.