After a total of about 3 days of practice with her harness, after which period she was performing nicely, I introduced the dogcart. I had fashioned a homemade lightweight rig from an old bike trailer. I took the bike trailer apart until all I had left were the wheels and the square, lightweight steel frame. I cut a piece of stout wire fencing/paneling and fitted it to the frame. Then I repurposed a pair of aluminum crutches for the shafts (notice that the emphasis is on lightweight).