The knots demonstrated in this how-to video are a good way to hang a hammock, because it makes it so easy to adjust your hanging height. The whipping knot around the tree will not slip if tied correctly. Make sure to tie the second half hitch or the knot may slip and come loose. As with all knots, use your own discretion and be safe. Watch this video survival training tutorial and learn how to tie some sturdy knots useful for hammock-hanging.