DURING A LOCAL FLIGHT, THE PILOT MADE 3 LANDINGS ON A 2860 FT RUNWAY AT SPORTSMAN AIRPARK. HE THEN LANDED ON A 2300 FT TURF RUNWAY AT CHEHALEM AIRPORT IN LIGHT AND VARIABLE WIND CONDITIONS. WHILE LANDING AT CHEHALEM, THE AIRCRAFT ROLLED BEYOND THE DEPARTURE END OF THE RUNWAY, CROSSED A DITCH AND ROAD AND CAME TO REST IN A SECOND DITCH. THE PILOT REPORTED THAT THE BRAKE EFFECTIVENESS WAS QUESTIONABLE. HOWEVER, AN EXAMINATION OF THE RUNWAY REVEALED SCUF MARKS FROM THE PLANE'S MAIN WHEELS, BEGINNING ABOUT 150 FT FROM THE DEPARTURE END. THE OWNER OF A BRAKE REPAIR FACILITY STATED THAT THE MARKS INDICATED TO HIM THAT BOTH BRAKES WERE ACTIVATED AND LOCKED. THE RIGHT MAIN GEAR FAILED WHEN THE PLANE CROSSED THE FIRST DITCH. AT THAT LOCATION, A SPRAY PATTERN OF HYDRAULIC FLUID WAS FOUND WHICH WAS TYPICAL OF FLUID UNDER PRESSURE. AN EXAMINATION OF THE BRAKES REVEALED ONLY NORMAL WEAR.