Put yourself in his shoes. Think like a horse. Remember, a horse will be scared out of his wits over a horse-eating butterfly!
If you were were afraid of heights and standing at the edge of a cliff and a friend came up behind you and gave you a push (just for fun), how do you think that would make you feel? And what if that friend did it every time you were near an edge? Sooner or later you are going to turn on that friend and let him have it, aren’t you?
You are like that friend to him. So stop pushing! The first thing you should do is get off so you can be safe, or he’s going to take matters into his own hands (or feet) and sooner or later he will flee from danger because that’s what his genetics have bred him to do. Then, do advance and retreat until he is able to move past whatever is disturbing him in a relaxed manner. Respect his fear and take the time it takes, not rushing him.
Do this every time he hesitates. Soon he will realize you are taking care of his needs and putting him first by making him feel safe because you are not pushing him over the edge. You are making him braver and his spookiness will subside because he will trust that you won’t put him in the way of that horse-eating butterfly. You will have become the leader he needs.