The harness I got at a local pet supply store, the cart is a friend of mines. Unfortunately, I can't afford my own at this time (she got it from someone in San Diego who makes them, but they are like $600). I had a friend make a cart, but it is not strong enough to hold a person, and I made it just to practice. This weekend I hooked Kai up to my friends cart and we put a person on it. He did great while I led him, but was not ready for someone just to "drive". I will add a picture of my cart after sending this message.
I find that carting is good exercise for Kai, because it not only works him physically, but mentally as well. And when I go to dog shows or fun matches and stuff, I put his crate, my chair and all the stuff on the cart and make him haul it to where I am going to set up.
Thanks a lot Kais mom, I always though it would be a good idea for my dogs to haul me around instead of me always 'hauling' them around. lol. ANd I'll bet it would be great exercise as you say. One of my pups owners has her Skiijoring, pulling them on ski's and in their sled too. SHe loves it, she also carries a pack when Hiking to carry her own blanket and food.