here's the setup we have...
Here are closeups:
the locking carabeener is in that mess of extra chain. we kept extra to raise and lower the spring pole
The connector rope added an extra foot between the spring and the tug rope. I can also loosen the knot and get the tug rope off if I want to. It's nylon so it's much stronger than a cotton rope of the same size. I didn't want the dogs chewing on nylon so we got another rope for the actual 'tugging' surface
The chewed end of the tug rope. It's about three feet long and had three knots in it. the bottom knot is mostly gone and has been re-tied a few times. The bottom of the rope is about 4 feet off of the ground.
It is about 8 feet to the base of the spring, to prevent the dog from biting the spring by accident.
Let me know if you have any questions....