When I started Tris, I focused on ground work exclusively for about six months. He didn't trust people, was aloof and hard to catch, was headshy in the extreme, and was not yet confirmed in basic things like standing to be groomed, picking up his feet, and so on and so forth. I put a lot of time and effort into his manners and his handling from the ground, and it has really paid off. He is generally a pleasant, obedient horse to handle.
There are a few voice commands that I have instilled in him over the years, through a combination of praise and repetition. We re-visit them every few months, starting with me standing at his shoulder and proceeding to him out at the end of a lead rope, and last night was one of those times. He was so pleased and interested to work with me that I'm going to try to install a few more over the coming weeks, perhaps with some clicker training. He's so smart, and it's so nice to be close to him once again.
Here are his current voice commands:
"whoa" - usually a long, drawn-out "hooooooooo" in a low, deep voice. This means stop in your tracks. I use it mostly in hand. The #1 rule for this is that he can. not. ever. throw his shoulder in to me when he halts. It has to be a square halt, not leaning into my space, not reaching over for a treat. He doesn't get praise until he stands square, in his own space, and not turning his head toward me. If he turns his head or shifts his weight I make him step over and we start again.
"walk on" - means start off again, at a walk
"step up" - means take one step forward. This is an especially useful one for getting him on the trailer. It's confirmed enough that it will go through his brain even when he's being stubborn, and often getting him to take that first step forward puts his feet on the ramp. I keep a clear distinction between this and "walk on" - I will use multiple instances of "step up" in a row but never let him take more than one step once I've given him that command. If I want him to keep moving I use "walk on."
"easy" - long and drawn out and a little bit low, "eeeeeeeeasy." I use this most often under saddle; it's his cue to calm down, re-focus on me, and not go haring off. I put it on him when we were first learning about riding in the open; he would go into a jackhammer quick trot that was wholly unproductive. It can backfire on me and make him too slow, but it's too useful to be able to bring him back for me to worry about that too much.
"back" - the usual: take a step back. This is by far his worst one, and he doesn't do it well in hand or under saddle. I've worked on it a lot over the years, and the only place I get it consistently is when he's in his stall: he always has to back before I give him hay, grain, or a treat. He knows to "back" and stay back until something is in his bowl. In hand or under saddle he doesn't give a straight back, or he will ignore the first few. This is one I use a lot to re-focus him when we're doing in-hand. Sometimes when I'm doing something as simple as leading him back to pasture I'll stop and make him back, then go forward again.
"ssssss" - a hiss like a snake; his all-purpose "cut that out" noise. Usually a quick "sst" is enough to make him stop what he's doing. For some things, like his pawing, it usually takes multiple attempts.
"trot" - the obvious
"trot on" - c'mon, actually properly trot forward, mixed with clucking
"canter" - higher tone of voice, usually "can-TER!" and mixed with a kissing sound.
"walk" - when it's just walk it means slow down, long and drawn out, "waaaaaalk."
I also do a noise that's a sort of tsking mixed with a clucking, with my tongue against my top teeth, that's his "hey, pay attention, I'm over here" noise. I use it when I first enter the barn, when I'm getting his attention out in the field, etc. He can pick it out from pretty far away, and he always looks up and around for me.