Fit your dog with a cart-pulling harness. This special harness has extra padding and comes low across the dog's back legs to distribute the weight for pulling. If it's a weight-pulling harness, there may be a special bar in the back to keep straps from squeezing the dog's legs as he pulls. Once he is pulling at your cue, start adding bits of weight to the cart. Toys or rocks work well. Eventually the cart should be pulling weight as heavy as the kids or stuff you want him to pull around. He should follow your commands respectfully, especially "Stay,"...