Hand refuses to stick to forearm bone

Hi, I am really loving the tutorial but having some minor issues keeping things all together.  While posing and manipulating the arm,  the hand and IK control bone for it keep moving and stretch crazily. I successfully did the copy location constraint with the foot bone and the foot/leg control IK bone, but cant seem to get the same to work with the forearm bone and the hand.  Thanks for any help.