Rebel is a great horse. I trust him with my nephews, with people who haven't ridden before, and (aside from that whole gate incident with Stingray) he's never let me down.
This last week I discovered a personality quirk, though. It seems that while Rebel is ok with leaving the other horses, he's not ok with being left. This was exacerbated by the fact that we'd turned them out on a farm field just chock full of fallen grain the day before, and the horses and cows had gotten out. I tracked down the horses (a mile away, yeesh) and got Rebel caught and saddled with no problems.
The issues started showing up when I got on. I got behind the other horses and encouraged them to start moving back towards home. They, of course, were feeling frisky and trotted off a little ways.
No biggie, I'll just ease up behind them and... what the hell??
Rebel went neurotic. Sidestepping and tossing his head and generally making it very clear that he is not happy with this situation. So, I got off and grabbed my spurs. He wasn't wanting to listen, so I needed the extra encouragement.
Once we caught up to the other horses, he was fine, and he was fine with leaving them, he just doesn't want to get left.
It wouldn't have been such a problem with Rebel, I'm sure, if he didn't have so much excess energy from munching on fallen grain all night, but since he did, there came a point where he became flat out dangerous about it.
I had to find a good place, both physically and metaphorically, and get off and walk.
There are a lot of personality quirks out there like this. And, it's not that uncommon for a horse to not like to be left behind by his buddies. More common is not wanting to leave his buddies at all. This behavior is commonly known as "buddy sour" or "barn sour."
It is a fixable behavior, it just takes work. For a buddy sour horse you have to consistently make them work while they're near their "buddies." This can be either a particular friend, or just any other horse, depending on your horse's personality and what they've gotten away with in the past.
You need help for this, since you need a buddy, so recruit a friend. If your horse is buddied up to a particular horse, try to use that horse. If the buddy is also sour, you may want to work one at a time, with a calmer horse that will be able to stand still while you're working the other horses near them.
If your horse only has this behavior under particular circumstances, you need to re-create those circumstances. If he's buddy sour on the trails, you need to train on the trails, if it's the arena, train in the arena, etc. If he's just buddy sour in general, you can train wherever you're comfortable.
First, have some fun. Warm up, trot around together, do some figure eights and serpentines and just make sure your horse is paying attention. Do this in tandem, if necessary, because working while another horse is near by is just fine, it's a behavior you want to encourage. When you're all warmed up, have the other horse stop, and keep your horse going. If you get ten feet or so between them before your horse starts to rebel, stop your horse and make him stand, away from the other horse.
Then go back to the other horse, but don't stop this time. Trot your horse in small circles near by, or around the standing helper horse, if you can do so safely. Let's not get horses kicked, folks, that's never any fun. If you're trotting around the other horse and he's displaying signs of agitation, move to trotting in small circles close by.
Your helper needs to stay alert, and be ready to get out of the way if your horse stops listening, shoulders out of or into his circles in an attempt to get closer to his friend, or has a real fit. Be alert and safe, as with all equine related activities. But for the most part, your helper can just sit there and relax.
Work your horse, trotting, not walking, we want it to be hard enough work to make being elsewhere and standing still preferable to being with his buddy and working, until he starts wanting to slow down and relax. If your horse is one who will quite willingly slow down after three strides of a trot, work them longer than that, of course.
At this point, you want to come out of your circle and get headed away from the other horse, then drop back to a walk. Walk a little further away than you were the last time you stopped, and have your horse stand. If he'll stand calmly, praise and pet him and relax a bit for a few minutes. If not, simply keep him from going back to the other horse for a minute or two, and then trot back to the buddy and repeat the process.
Doing this consistently, and you can use this method while you're out and about if your horse starts acting buddy sour, will convince your horse that being away from his buddy, and going away from his buddy, is less work than throwing a fit, even a minor one, gets him.
If your horse can walk calmly with the other horse on the trails and only throws a fit when you ask him to go away from his friend, then ask him to go away a few times during the ride, and repeat this process until your horse will leave his friend willingly.
This process also works with barn sour horses, with the variation being that instead of another horse, you make your horse work when he's near the barn, and let him rest when he's away from the barn.
I've seen this method click with some horses almost instantly, but there are no magic wands. Expect to continue this training for a while, until your horse will willingly do what you ask, whether he's pointed away from his friend or not.
For horses sour about being left behind, change things up a bit. Have your helper ride away, and when your horse starts having a fit, let the other horse keep walking, but trot your horse around them in a circle. This takes a little coordination and keeping your head in the game, but it's imperative that your horse associate following a moving horse with a lot of work. I would stay in the arena or corral for this method as much as you can.
Also, make your circles more elliptical... stretch them out in front and in back, but stay fairly close on the sides. This helps both with keeping the two horses from colliding, and also with making sure your horse associates the work with following the other horse.
Again, when your horse starts to want to slow down and take it easy, stop, and let the other horse continue walking away. If your horse gets antsy, repeat. If he stands calmly as the other horse leaves, praise him and let him relax. Here, I'm going to say that if your horse stands calmly when the other horse gets outside his normal comfort zone, have your helper stop.
It's very easy to undo good training by trying to push it too far, too fast. The whole point of this is to convince your horse that the world is not going to end if his buddy/the barn is too far away, so increasing his comfort zone slowly until he can be out of sight of the object of his affections will give you a solid foundation.
In the long run, it's better to do things slowly and gently, working with the horse's own natural inclinations (because let's face it, what horse wouldn't prefer standing and getting petted to working his butt off? those small circles aren't easy at the trot) than to push them too hard, and you'll build a great working relationship with your horse at the same time.