If you need help, get people who can be patient and see this as a fun training activity. If your horse is a stallion, you might get a good crew to help you or creatively arrange a safe way to use an estrus mare as the carrot. Most stallions with good libido typically appear to forget about minor novel obstacles when a breeding opportunity is on the other side. Sometimes the regression comes right after a day of great progress, so if you're not expecting it, you can be very disappointed. Just return to the last step at which he was compliant or relaxed and proceed from there.
Setbacks are almost always temporary, and the day after a setback typically has excellent progress.
Your job is to try to accept the setback as part of the progress. Human frustration and discouragement can rub off on your horse. Your relaxation and quiet persistence toward the goal will enhance the positive progress. You can have the obstacle set up near the outer perimeter of the line or pen. You can get the horse going inside, then gradually work out to the obstacle path.