The first thing I've seen is how many people think their horses (or dogs) know voice commands but in reality the animal is responding to body cues that the person doesn't even realize she is giving. The story of Clever Hans illustrates how well horses observe our body language (if you don't know the story, you can google it easily). Like a lot of people, I talk to my horses but now see that most of what they hear is, "blah, blah, blah, blah". They might be able to pick up something from my tone of voice. When longeing horses, I was taught to use a crisp, upward swinging tone to encourage a horse in an upward transition and a low, slow voice for downward transitions. If you think about this, then the horse really doesn't know the word. Others who do this: do you say "trot" the same way whether you are asking for it from walk or from canter? More importantly, I think if anyone videoed me longeing a horse it would be obvious that I am also using body language to affect the horse's response. Some Natural Horsemanship methods employ this but they use very obvious movements- not for the sake of the horse (again- see Clever Hans!) but for the sake of us humans who need to be obvious or we'll screw it up!
If I am going to transfer my voice commands from the ground to under saddle- which is my purpose in teaching this before getting on- I won't be able to use my visual body cues because Percy won't be able to see me. So I need to teach this carefully and test it thoroughly to be sure he is responding to my voice and not something else.
In hand, Percy walks off promptly when I walk off. So he is responding to the visual cue of my movement. Some horses wait until they feel a pull on the lead to walk off. Some horses have to guess which their person wants from day to day. In beginning to teach him voice cues, I follow the rule of
new cue -> old cue -> behaviorDone repeatedly and consistently, Percy anticipates that when I say "walk on", I will then walk. I start to see his body begin to prepare for the walk as I say "walk on". I am very careful as I do this not to combine the new and old commands. I don't want to say "walk on" AS I begin to walk, because then the words become "blah, blah, blah" as he is really responding to my body (a horse's easier and therefore preferable way to read people). I want to be very still with my body, maintaining a forward position just as I if would if I were expecting him to stand still next to me. But when I saw his body prepare for walk from my words, even though my body hadn't changed, I knew he was anticipating that walk would come next.
in this case: voice command immediately followed by walking off
This is similar to our newest Jack Russell Terrier, Eloise. She came through a rescue and previously lived in an apartment, always on a leash when she went outside. As a result, she learned to LOVE her leash because she LOVED to go outside. So when the leash consistently and repeatedly was followed by going outside, the leash became a cue for going out! I find this very funny because I've never had a dog who liked a leash before! My older Jack Russell, Beetle, Hates his leash. To him, it means being constrained because he grew up off leash and when he sees his leash, he gets very depressed. The presentation of the leash became a very different cue for these two dogs. Also important to note is that even though Eloise is now off leash almost all the time, she still LOVES to see her leash and gets very excited. She doesn't like to be on the leash (she pulls and pulls) but seeing me pick it up still elicits real excitement from her. Her early and consistent lessons have stayed with her.
So, back to Percy. I want him to respond with enthusiasm when I ask him to walk on. Preferably not as much as Eloise with the leash (!), but I want him to walk off willingly and happily, not sluggish and unsure. What made Eloise so enthusiastic? Positive reinforcement! Going outside was hugely rewarding for her. Luckily, Percy is a temperament that likes to move so walking off is rewarding, but I can add more power to that with the click and treat.
I have not been clicking and treating to this point because walking off with me was taught when he was just a weanling- I haven't had to reinforce that for quite some time. And when I added the verbal cue, initially he was still responding to my body, not the voice. But when I see him begin to move, even a tightening of his muscles and or a lean of his weight forward, in response to my voice- before I move my own body, then I click and treat. I am reinforcing the fact that he responded to my voice.
At this point, (which is where we are spending time right now), I am being as observant as I can. I always preface walking off with the verbal cue. If he moves before I do, I click and treat. If he doesn't respond, I simply walk off with him. I also have to watch to be sure that he doesn't walk off without any cue. Practicing this, horses sometimes just learn walk-stop-walk-stop. They aren't responding, they have just learned the drill. So I stand for different amounts of time before cueing him. If he moves with no cue, I quietly slide my hand down the rope and ask him to stop and back up...no unrequested forward! He is learning that if he responds to the verbal cue he gets a CT and is becoming more and more responsive to it.
When I do get on him, it will be a different situation so I will be very rewarding when he responds. But taught this way, I am confident that he really does understand that "walk on" means walk (and I will teach, whoa and trot and canter the same way). Then I can transfer "walk on" to a leg aid, in the very same way. At that point the verbal cue will be the "old" cue and the leg aid will be the "new" cue. So I'll apply a little leg and immediately follow it with the verbal cue. As soon as he responds to the leg aid before the voice command, he'll get a CT and we'll be on our way.