My TB has good ground manners, but every once in awhile he decides he doesn't want to go forward anymore. For example, when I lead him to the grooming stall at the barn, he always stops. I will then turn him in a circle and step back into the grooming stall. Sometimes he'll follow. Sometimes he won't, and I either have to try to walk him to the other grooming stall (which he always goes into it) or I swing the lead rope around a little and that convinces him to start walking again. He also does this sometimes with the wash rack. Sometimes he goes in and other times he plants himself. What can I do to get him to continue following me?