Growth opportunities abound

I know a decent amount about horses. Not compared to a professional, or someone who's been riding their whole life, or, ok, lots of people. But compared to a beginner, I know a lot.
But horses, one of the best and worst things about them, is the constant challenge. And man oh man is Willig good at that. As soon as I start to relax, he takes me by surprise again.
Last night, I lunged him outside while they brought in the last of the horses still in their turn-out. And he did ok with that. And then someone hauled in to ride, and rode past him into the woods, and he did ok with that. And it got to be dusk, and he did ok with that.
But then, two people came across the field from a trail ride and went into the barn, and then, he just had done so well with everything else, that old herd bound thing kicked in and he just couldn't deal with it anymore. I tried riding him, but couldn't get him to focus, so I got off him and lunged him and he did the thing where he broke into crazy nervous sweat and raced around with his ears just FIXATED on the barn and not listening to me and not paying attention.
After a while, his ear started flicking towards me, so I rode him again, and every time we came around the corner pointed towards the barn, he'd try to rush, so we'd make little circles - little circles - little circles - then try again. After about 5 laps, he quit rushing, so I just let him quit then.
We didn't get to work on any of the things I planned to work on, and while we've made good progress if I look back, it feels frustrating to not ever just - well - ride.
I know I'm learning a lot, and in an area I didn't know before, but I really, really wish I had a trainer right about now.
And, of course, he's not getting as much time as I wish he was because of my new position at work and Odie's heart.
I need to get some books about what to do about a herd bound horse. I've just never dealt with it before. All I can think of is ride him (or work him) until he behaves, then stop. Then keep introducing new things until he builds confidence. I'm just in totally uncharted territory (for me).
The wonderful thing, however, is what my co-worker and riding friend said today, about riding horses, even when they're naughty, makes you be present. It's true. Just like climbing. It is the single easiest way for me to be present. It's why I love it so much. Well, one reason.