Step 1: Stuff you will need
An generally big ovalish shaped rock. (this can vary but this shape seems to work best)
duct tape (some of my favorite stuff!!!)
and some string. (Nylon if you have a choice, it doesnt flay as easily)
Step 2: Starting out...
then cut some string (about the length of your arm is good but it can be longer) and duct tape it to the rock.