Learn the difference between riding your horse through a properly executed corner and a properly executed curve. There is a difference in the way a horse performs a square turn vs. a curve. When you talk about making square corners, your horse has to keep his body straighter and more in alignment. You want the horse to keep his head in front of him.
You want your horse to ride to the corner and then simply square up to turn. If he’s making a left turn, he moves the hind end, his hips, to the right and brings the front end, his shoulders, around to the left. You push the hips to the outside and bring the front end around the corner.