All aircraft should be secured when left unattended. Regardless of the conditions, parked gliders should have the wing into the wind secured, spoilers opened, flaps retracted, and the canopy closed and locked. On windy days (15+Knots) any unused aircraft should be put in the hangar or tied down.
Further, when securing the aircraft, two people are necessary, one to stay at the wingtip until the weight arrives, and one person to open the spoilers and secure the canopy. Even on apparently calm days, a thermal gust can happen, so the person at the wingtip should wait there and someone else should get the weight. When the gust arrives, it will not matter if you are close to the glider, or if you at the other side of the airfield, the result will be the same. Someone must be at the wingtip to prevent the glider from damage and the canopy must be closed an locked.