Been there, done that!
On Lake Mead, threw my 1st "new" box anchor out, line was tied and all. Boat held for a couple of hours in a pretty stiff wind. When we went to leave, pulled the line and the dummy that tied it to the anchor (ME!) didn't do a very good job and all i got was rope! My 2nd "new" box anchor has a hell of a knot on it now....
BTW, looking forward to our annual trip to Powell in July...