A CESSNA 140 NOSED OVER IN A DITCH AFTER ABORTING A TAKEOFF. THE PLT INDICATED HE WAS PRACTICING STOP AND GO LANDINGS. DURING THE LAST LANDING THE RIGHT BRAKE WAS INADVERTENTLY APPLIED AND THE ACFT VEERED TO THE RIGHT OFF THE RWY. THE PLT INITIATED A GO-AROUND BY APPLYING FULL POWER. THE ACFT WAS OFF THE RWY WITH THE TAKEOFF GROUND RUN TRANSPIRING ON RIGHT SHOULDER. THE ACFT BECAME AIRBORNE APRX MID-FIELD AND THE PLT CAUTIOUS NOT TO STALL THE ACFT LEVELED OFF TO ALLOW THE AIRSPEED TO BUILD. THE PLT THEN NOTICED AN APPROXIMATELY 4 FT TALL FENCE AND JUDGED HE HAD SUFFICIENT ALT TO CLEAR THE OBSTACLE. AS HE CROSSED THE FENCE APPROXIMATELY 220 FT FROM THE RWY CENTERLINE HE HEARD AN UNUSUAL 'TWANG' NOISE AND ASSUMED HE HAD STRUCK THE FENCE. HE DECIDED TO ABORT THE TAKEOFF AND LANDED ON THE RIGHT SHOULDER OF THE RWY. DURING THE LANDING GROUND ROLL, THE ACFT PLUNGED INTO A 10 FT DEEP DITCH AND NOSED OVER. A POST ACCIDENT EXAMINATION OF THE ACFT REVEALED BARB WIRE ENTANGLED ON THE TAILWHEEL.