Lynn Orbison and I have gone partners to buy a used Sacco cart to help with training our dogs during the "off" season. The Sacco Cart is a very light weight, four-wheel cart with shafts or either one or two dogs. It is unique because it has a steering mechanism that allows you to steer the dogs, rather than steering the cart. This should be ideal for off-season "gee/haw" leader training.
We've been training some of the dogs to pull it during the few hours when the weather is cool enough to do so. Some of Lynn's dogs already have experience on this type of wheeled rig, and they were happy to demonstrate just how much fun it is for both dogs and musher.
This cart is the neatest thing since canned beer. Although you can only run one or two dogs at a time, the dogs get a great workout, it's easier to work on lead commands using the cart, and it's a lot quieter and sometimes even faster than "motor-mushing" on a motorized four wheeler.