not only is it a double fisherman's bend, but it's not that difficult to untie. grab each knot and pull them away from each other, then loosen and untie each knot separately. it's not that it's hard to untie, it's hard to decipher by looking at it because you think it's one knot, not two knots pulled against each other.
http://www.youtube.com/watch?v=ESo9FZuIAHo
I can only do sailor knots...