I am considering getting a cart harness for Butch, my 14 month old GSD to pull a little red wagon with big inflatable tires. I love for my whole family, including Butch, to go on walks but my youngest son, who is 3 years old, gets tired after about 3/4 of a mile. Butch is a very strong and pretty big dog and I don't think he would have any trouble pulling it. I would pull it myself, but I have Butch on a leash and my wife is usually walking Lucy, our little mixed breed pup. My oldest son, who is 5 years old, is so energetic that he has no problem walking with us, but he is too little to have to pull his little brother in that wagon. Have any of you ever used your dogs to pull a cart? Personally, I think Butch will enjoy it but I have never done anything like this and really don't know of anyone else who has either. Any advice?