Recently my boy has started pinning his ears when he's in his stall. He's only been stalled for a little over a month now - prior to that he'd been pasture boarded his entire life (he's 6, I've had him 1 year now). But even with a stall, he's in about 2 hours/day, one for breakfast one for dinner - the rest of the time is on pasture with a herd of 6.
Just the last week or so he's started pinning his ears at anyone who comes towards his stall, but then puts his ears back up as soon as they get close.
I groom and tack him in his stall, and mostly he just lets me come and go, but occasionally he's started pinning his hears, squealing, and kicking his heels up a bit (only maybe an inch - just a threat, so far - I don't want it to escalate to more than that)...
Mostly I've tried ignoring it, in which case it's over as quickly as it started, and he just puts his ears back up and acts like it never happened.
A couple times he got a little too close with his hind end and I pushed him away/made him move until his ears went back up. Then I let him relax.
During this same time, he's also started being the "big man on campus" out in the field. He used to be mostly a loner or just flit around among other horses, near the bottom of the herd structure. But lately he's kind of ruling the place. The barn manager has been making comments about it.
I want to put a stop to it before it gets any worse. Any suggestions on the best approach?
Yes, you do. He is an aggressive horse (personality) and will bully the herd as he has begun to bully you. The herd leader needs to be the best behaved horse in the barn.
My original herd leader (6 horses in that herd) was a spastic, troublesome horse to handle and ride, and he would frequently blow off steam by making the others run and picking on the weakest members (an older mare and a pony.) When I bought my best herd leader, a 15 yo QH/TWH cross who looked like a fuzzy, palomino milquetoast, who anybody could ride and had TB pony horse in his resume, I put up a temporary fence for him bc I thought my leader was going to beat him up. The next morning morning the fence was down, "Tyke" had taken over, eveybody was calmed down and my previous leader, "Dusty" was cowering in the corner. Tyke would let the mare and pony eat with him and he ended up being the toughest horse I have ever owned or ever witnessed--EVERY horse he came across backed down to HIM! (just an aside)
It is NEVER acceptable for your horse to ever kick at you. He's behaving as if you are another horse. If he kicks another horse, that horse will move away and graze someplace else. If he kicks YOU with the same force your leg or arm will break. I also suggest carrying a short whip that you can slip into your boot and have it at the ready. Next time he kicks at you, smack him on the leg and teach him the word, "NO!" (This will come in handy in the future, too.) His attitude WILL improve as you establish authority. Don't let him become a "Dusty", who was a little monster. BTW, he got loose after I sold him to somebody else, ate 1/2 a storage can of grain and died of colic. Your horse needs to be obedient in every way, if you want him to live a long and productive life.