When Going Behind A Horse, What Should You Do?

Make sure the horse knows that you are there. A startled horse will kick as a natural defence.

That's about what i was going to say . Walk far enough behind so the horse can not kick you if they have a twitch.

You should walk as close as possible to them if you are walking behind them. A horse that is going to kick you when you are that close, can only bump into you. When you stand farther away, you risk the horse backing up to get a better shot at you.
Begin by their withers and sweep your hand down his back as you walk towards his rear, and keep rubbing him and talking to him letting him know you are there as you pass by.