You can choose to leave the rope on the ground, or toss it over the horse's neck. Whatever way you prefer, do it consistantly. At the same time, tell the horse a firm Whoa. Then walk away. I prefer not to back away from the horse as I find that it draws the horse with you. Turn your back and move away from the horse. You'll have to be very keen about watching your horse as you move away. Don't look directly at him - which could also draw him towards you. Use the shadows to tell if he's moving, listen for his feet moving on the ground, look out of the corner of your eye, etc. Any time he takes a step, you need to immediately turn around and charge toward him - do whatever it is that you do to get him to move his feet but without touching him or grabbing the lead rope. I stomp my feet, wave my arms, etc. while moving towards the horse, and I continue doing that until he moves his feet backwards. He should end up back in the same spot that he started from. Again, without touching him or the lead, I will stop my body language and tell him to Whoa, then walk away again. Keep repeating until the horse learns to stand without moving his feet. I would not ask him to stand for extended periods of time when you are first teaching this, just a minute or two at a time.
This skill comes in handy in so many ways. One time, I had a horse in training that I told to stand ground tied and I went over to help someone else with their horse, which turned into a long process, but that training horse stood quietly still where I put her and I nearly forgot about the poor thing! She was unattended for about half an hour! She got lots of praises that day. Another time, I was on a trail ride with a small group and one of the ladies needed to get off of her horse for some reason (can't remember why). I had trained her horse so he knew how to ground tie, but I don't think she ever asked him to do it. After she dismounted, she left her horse standing in the middle of the trail and walked over to another rider. It took probably 5 minutes before she got back to her horse - but he never moved his feet once during the time he was left unattended. I told her it's a good thing he knows how to ground tie otherwise she could have been chasing him down the trail all the way back to the trailers!
The first part of this video shows what I would expect from a horse that is ground tied.
One thing to consider before you teach your horse is his maturity level. Usually horses about 3 years old and older are ready to learn this skill. I have a yearling at home that is not ready for ground tying, but most other horses I've worked with are ready for it when they are 2 1/2 years to 3 years old. It should be really easy to teach this to an older horse.