I have also done this with a 2x4 and a bipod made of two fence poles and a Eye-bolt in the center. It takes a lot of swaying to knock it down.
Yosemite Sam: Are you trying to make me look a fool?
Bugs: You don't need me to make you look like a fool.
Yosemite Sam: Yer deerrrnnn right I don't!
Interesting, I shall try it out.