Automated dog tug of war

Dogs are willing to invest a lot of energy in tug of war. I wonder whether it's possible to get it started, and then leave the dog to it, to save the ower the effort (and perhaps generate energy at the same time). In a non-energy generating solution, all that would be needed is a bungy rope (as used for bungy jumping) and then a length of dog-proof rope on the end. Once the owner initiates the dog's interest, the bungy would (hopefully) sustain it by pulling back. An energy generating derivative would perhaps use the same concept, but also attach the rope to a chain driven energy-generating flywheel (like a rowing machine).