In reply to Paul R:
Haven't done it on a sport route, but with a trad route I rig my upper anchor with decent rope protection on any edges, then ab down and find a decent anchor around 1.5 - 2 metres off the ground - I clip the rope through this, then attach a weight to it i.e. boulder mat, bag etc.
I rig it so the mat is hanging just above the ground, with a decent amount of slack between it and the anchor. This means that if you swing out from an overhanging route you can simply pull the rope and you'll move back into the wall, whilst still allowing you enough slack for freedom of movement with the rope.
I also use a chest harness made from two slings larks-footed together and then clipped into an HMS screwgate with the shunt in the centre, and then attach it to my harness with a quickdraw dogbone sling and another screwgate.
This combination means that the shunt sits up near your chest, so if you fall you are simply weighting the shunt rather than falling onto it dynamically from above, thereby negating any slippage that could occur from a sudden fall above the shunt.
The chest harness also supports you and stops you from tipping backwards during a fall. To escape from the rope if you can't top out, just attach the belay device below the shunt and then take it in until it is close to the shunt. Then, pull the cord on the back of the shunt to release it, and abseil on your belay device as normal whilst holding the shunt open.
In a sport climbing scenario I imagine that you could simply use a bolt/draw in place of a trad ground anchor. Hope this helps!
