Horse people are always looking for a way to contain horses; stalls, barns, fencing, halters, bridles, bits, martingales, side-reins, longe lines, trailers, lead shanks, and so on. Horses are meant to be roaming creatures. As domesticated animals, for their own safety, and that of those around them, there has to be a way to restrict the roaming. In best scenarios, horses would have stalls they could enter and exit at will and acres of pasture. Most horse people are not able to provide best scenarios. There are terrible scenarios, adequate scenarios, good scenarios and over the top -ridiculous scenarios. Now, I hope I never have to type the word scenarios again.
As closely as possible, we have a responsibility to our horses' well-being to mimic their natural environment. Which includes, not only housing them, but communicating with them as well. The aids we use when riding all have to be taught to horses. They have an amazing capacity to learn so it's just marvelous the things we can teach them. With that, we have to be careful because sometimes they learn things we don't want them to.
At my stable, I teach every horse to give to poll pressure and lower it's head. This makes putting on and taking off halters and bridles safe and easy for everybody. The horses don't get their teeth clanked by the bit and riders/handlers aren't tossed about or yanked off their feet.
Giving to pressure doesn't mean that we physically move the horses, that's just brute force. No one will ever be able to out brute force a horse. Well, maybe if it was a really big guy and a wee little mini horse, but that's not the general situation. When I teach horses to give to pressure it's so that they completely release and relax their bodies, not so that I'm holding them in a position or making them do something. I'm going to stick with the poll pressure example because otherwise I'd get rambling on and we'd be here all day. I don't know about you, but I have got other things to do.
To teach a horse to lower its head, I apply firm pressure with the palm of my hand to the poll just behind the ears. At first horses will resist and try to press their heads upward. If they come up I maintain the same amount of pressure. When lifting the head doesn't get the response they want, they'll try going down. As soon as I feel the horse attempting a move in the right direction, I release the pressure. This is highly important. My hand must not continue downward with the horse's head. If it did, the horse would not get the release and would try moving in another direction. After the initial correct response, I ask again: firm poll pressure as soon as the horse drops his head, I release the pressure. it takes just a few minutes for horses to figure this out...if you ask correctly.
What goes wrong is when the horse's head is pushed down. Then the horse hasn't made a decision so he hasn't learned anything. If the horse drops his head but comes popping back up as soon as you take away the pressure, he never truly gave in the first place. If his head goes down but his muscles hold tension then he hasn't given to the pressure. Once he understands the cue to lower his head, then you can wait before releasing until you feel softness and relaxation through the horse's neck. If a horse is very tense you can help him find his way by placing your other hand over his nose and gently rocking his head back and forth. This helps him to unlock his poll and loosen the muscles of the neck. It's all about the horse being calm and relaxed, not about forcing the horse to submit.
Once you've established the cue and the horse is consistent, don't forget to ask for the head down from the horse's other side and also at different places around the barn (in the stall, in the ring, in the paddock...) otherwise you will have only taught the horse that he should lower his head when you stand on his left side, in the barn aisleway.
This exercise is one of the most valuable assets to working with horses. It takes all the fuss out of bridling, clipping bridle paths, braiding forelocks, even just walking down to the paddock. When Raffles gets in one of his spooky moods - before it escalates too far - I can stop him, ask him to put his head down and relax for a minute then continue. It doesn't work 100% of the time... sometimes, he lowers his head, lets out a big sigh and then immediately leaps back with eyes like saucers ("Did you see the size of that butterfly?!!?!?") but it's generally effective when he feels like a coiled Spring and I want to avoid the sprung.