funny you mention that, because i was playing with the staff sling earlier today.  i found that it works quite well if you just tie two half hitches in one end of the string to secure it to the end of the staff (about 2 inches from the end).  i then figure out where to put the loop.  i make a loop of the right size that can fit with lots of extra space around the staff.  sline the loop over the end of the staff and down to the other loop.  place a stone in the pouch and sling away.