Pay close attention to what the helper says instructing you. He expects you to do exactly as he says. His safety, yours and your dog depend on it. He says be a post, it means you do not move, no shuffling feet or moving from your position. Be sure you have a very solid grip on the leash. A good way is to make a slip loop in the handle and slide your hand through. Wear a light leather glove over this and it is nearly impossible to get the leash off your hand.
He may tell you to let the dog go at a certain point so be ready to release the leash so you will,have to take the glove off and get a good grip on the leash instead.
You will probably be surprised how hard the dog can pull.
Let us know how it goes.
Tron GSD SCH III, AD, TD. Never to be forgotten buddy
SCH III Club
Samantha, Australian Shepherd, rescued , loves everyone