Take the handle off of the child's wagon, leaving the hitch in place. Where the handle base slipped through the now-loosened hitch, thread the "U"-shaped aluminum conduit pole, starting on one side and moving your body with the pole so that you always have a firm and balanced grip on the metal. If the metal slips, your hitch will not retighten correctly and you could risk injury. Once the pole is in place, tighten the hitch as much as possible while holding the piping parallel to the ground. The piping should stay parallel.
Tie a Prusik knot at the base of your "U"-shaped piping where the hitch to the wagon is. Fold your rope in half, and place the loop on one side of the bar so that it rests squarely over the hitch, flipping the ends over the top so that they drag down on the other side. Make sure the rope is at least 4 feet on either end. Thread the ends into the loop so that the rope is secured to the bar at the hitch. Thread the ends through the loop again to ensure tightness in the attachment. Then, pull the ends of the rope so that the knot does not slide. Having the hitch in the center of the knot will help keep it in place.
Loop the rope once under the piping on each end so that when the rope is pulled on the piping will lift slightly, easing the weight on the dog even as the pull of the rope increases pressure. This will keep the forces at work on the dog equal at all times and prevent undue stress on its muscles as it brakes. Loop the rope into the wagon from underneath, giving you two reins.
Slip the carting harness onto the dog. Place the ends of the piping into the harness on either side. The carting harness should be made for holding this piping and will have fitted pockets and tightening loops to secure them in place. The dog should now be able to pull the cart easily.