The glider pilot reported that, while being towed and approaching 3,000 ft above ground level, the glider's rear canopy opened. The glider pilot informed the tow airplane pilot via radio that the canopy had opened, and the tow airplane pilot informed the glider pilot that he would try to tow the glider closer to the runway. Shortly after, the glider entered an uncontrollable downward spin, and the front canopy shattered. The pilot regained control of the glider, and the rear canopy separated from the glider. The glider pilot made an extended right base and prepared for an off-airport landing. The flight controls were not responding properly, and the glider landed hard on the runway. The pilot reported that, after the accident, he found a section of the tow rope still connected to the glider and lodged in the rudder mechanism. A review of photographs of the airplane revealed that the tow rope exhibited overload signatures. Each airplane still had a portion of the tow rope attached to it after the tow rope failed. The glider sustained substantial damage to the composite fuselage.