Before I go into how to teach a horse to take the correct lead, let me answer the question of, “Why does it matter what lead my horse is on”. The answer is not because that is what the rule book says. It is because it is what is proper and beneficial to the horses movement, and it allows him to use his body in an efficient manner.
Lets look at roping horses first, why do you want your calf horse to stop and back up straight? That is easy, because if he backs straight, he can pull with all of his body and pull the calf back to you which saves you time getting to the calf. The key here is that he can pull with his whole body. So if we relate that to team roping and ask how is it most efficient for a header to turn a steer? The heading horse’s job is to turn the steer at a 90 degree angle and pull the steer so that the healer has a good shot sooner. The most efficient position for the heading horse to be in, is for his body to be pulling straight up the rope of the steer, and that can only be obtained if the heading horse is in the left lead. If the heading horse is in the right lead and turning left then he is pulling with his left shoulder and is not using his entire body. This causes soreness in the shoulders and eventually ducking off to avoid soreness. If he is pulling straight and on the left lead he is pulling not with his shoulders but with his hind end. Why do you think that the old timers rigged their teams of horses in front if the wagons and not off to the side? They can pull best when their body is in the correct position.
Ok, now how to teach them to pick up the lead that we want and not the lead of opportunity. Before I explain this, let me just say that this is not the only way, but one way. I use many methods, but this one works for most. You must keep in mind that we are teaching, and teaching is learned best with repetition and consistency. It did not take you one afternoon to learn your times tables in school. Instead, it took days. 5 times 5 was always 25, it did not change to 30 after two days. Also keep in mind the teachers voice did not get louder and scream at you for every wrong answer, which would cause you to get frustrated and quit. Good teachers will encourage participation with repetition and consistency.
I like to work on leads while the horse is still in the round pen. Plus for simplicity sake, this will keep you from trying to work on other things like guiding and being worried about making corners before running out of room. First, your horse needs to understand giving to the bit laterally or left and right, and needs to be moving off of leg pressure at the hip. Once you have these parts you can encourage your horse to trot going counter clockwise in the round pen, or to the left. We will be working on the horse taking the left lead, to work on the right lead just take all of these steps and reverse it. With your horse trotting to the left apply pressure with your right leg, not to take a lope yet, but just to get their hip moving towards the middle of the round pen. Then slightly ask for their nose to point toward the outside of the round pen or fence. Do not over bend them into the fence, you are only asking for the nose to point outside of the circle to open the left shoulder. This allows for them to reach with the left front end or lead leg. With the horse in this position, encourage them to trot faster and allow them to pick up the lope when they feel comfortable. Once they have picked up the left lead, allow for the nose to come back inside of the circle. Avoid pulling or bending the head to far to the outside of the circle because this will impede forward motion, which is needed to break into a lope. If the horse has loped off, but in the incorrect lead, just pull back on the reins to cause them to break back down into a trot and start the sequence over again. To get an idea as to how far to bend their head to the outside, I just want to be able to see their right eye if I am trying to get them to take a left lead.
Now, once you have gotten the horse to a point of consistently picking up the correct lead,(like three correct leads in a row) start to relax on the outside rein pressure, and ask with just the leg pressure keeping the head looking straight into the circle. If they go back to picking up the incorrect lead, go back to helping by turning the nose slightly outside of the circle. Remember, that a lead starts first with a side pass. When you are asking for a side pass to the left your horse reaches to the left with his left leg and crosses with his right. It only makes sense that when you increase forward motion in that maneuver that your horse will again reach with his left leg and depart in a left lead.