Hello i have a year and a half Rottweiler and he loves to grab and bite stuff, but outside he is just to strong for me now to play tug-o-war with i have seen on a youtube video some how they attached a spring into a tree with a rope on it allowing the dog to grab it but not able to touch his feet to the ground letting him tug on it. i was wondering if any of you had any ideas of what i could us to construct such a device ? or maybe there is already something made at some pet shop ? your suggestions are appreciated thanks.