I guess you would have to calm him first before you put the rope around his legs. Or make sure that the rope was really loose so he doesn't entangle himself in it.
They can get into some of the darndest messes can't they? A couple of weeks ago my mare was tied up in the barn. She wiggled around and pulled a step stool to her and was kicking it with her front foot kind of playfully. Before I could take it away she got her foot in the hole. She just picked it up and shook it off and I moved it. I didn't know it was any big deal but my trainer said that some horses would have paniced and sat back and she did good. I'm constantly having to watch her though. She's worse than a toddler.