pulley

is there any reason why I shouldn't use an anchor shackle as a pulley? If i'm pulling a tree over, and the bull rope is going through a block on another tree and back through a mid-line bowline for a 3:1 pull, I want to put the shackle on the bowline so there's no rope friction at the bowline...

I wish to climb with double rope technique using a pulley in the canopy. Pulley would be attached to a static rope anchored at basal. Which basal anchor is the best when using this technique? Thank you!