I did it! I got Walter's lead on! I had it in my hand, and he knew it, but I kept talking to him and giving him sugar cubes.
Then I reached under his chin and clicked it on. He bolted, to the left, then to the right, tried to run out of the barn. I just stood still and held my ground, all the while talking to him.
He abruptly stopped fighting me, then accepted another sugar cube. I immediately removed the lead then and praised and praised him. Whew!
I was worried he would be "traumatized" from our lesson and would be angry with me, but when I left and returned to his pasture, he came running over just like before. Double whew!
I have no idea what I'm doing, but I hope its a method that works.