Lucky - fit to be untied

I bought Lucky a tug-of-war rope the first day we got him.  He didn't touch the thing for the first two weeks and has started lightly gnawing on it in the last week and a half.

Last night, he went to town on the thing.  But he didn't really destroy the rope as much as he untied it... like a puzzle.

Lucky untied this rope with his teeth.
I would be much more impressed if he tied it again.