A guiding line is an independent rope system along which the load travels while being lowered by the main line. The guiding line is anchored top and bottom and a tensioning system at the most logical end is used to vary the amount of deflection. The guiding line is used to keep the load away from the obstacles by the minimum amount necessary. If the load were moving down a cliff face that I must not touch, then a few inches from the face is all the deflection needed. Once the guiding line is used to create a major defection, it is no longer being employed properly.
To construct the guiding line, build an anchor on the bottom, away from the cliff face. One end of the line will be anchored there and the other end will be anchored at or near the main system anchor. The tensioning system needs to be placed in a very convenient area; make sure you have enough rope for the deflection. The load is rigged for lower and the a pulley is attached to the main litter attachment point and rigged to the guiding line.
As the load is lowered, the guiding line can be tensioned and slacked as needed. This is not a highly tensioned system, so keep the load close to the face as possible and do not use this for long distance travel over less than vertical terrain.