Parachutes
Generally, glider pilots fly very much closer to other gliders. It is quite a sight to be in a stack of gliders all circling in the same themal. Ridge soaring can also bring gliders into close proximity to each other.
Obviously the risk of collsion in these situations is much higher, and wearing parachutes make a lot of sense. Every year there are sucessfull bailouts after collisions and in 1999 after a lightning strike destroyed a K21 at Dunstable.