Riders seeking advice systematically tell me they have worked through ‘every’ bit and nothing has been a permanent solution. Although some of these bits may have initially had the desired effect the horse has then resisted and found his way around it.
Many years ago I had a very extreme experience. I was given a ‘dangerous’ horse that would otherwise have been destroyed. He had undergone a regime of thorough diagnostic procedures that had ruled out any apparent physical cause. His party piece was to rear and on four previous occasions he had gone over backwards and hospitalised his riders. He was a potential event horse, a 16.2hh thoroughbred, grey and with very pinky lips. I took my time letting him settle in and discovered his skin was extremely sensitive, to the point where he could only be groomed with an extremely softly bristled body brush.
He was so sensitive, everything that came into contact with him had to be cushioned and padded. After much ground work and bonding I sat on him for the first time. To my great relief everything was great, and he was extremely willing and responsive. I obtained the same good result on the second day. However, on the third day after 10 minutes easy work he went straight up. To cut a long story short I discovered that he could not tolerate being ridden in the same design of bit for 3 consecutive days. Even though there was nothing untoward to see in his mouth, I changed his bit every second day. The problem was resolved and I called this his Comfortable Working Window. He went on to event successfully at a very high level.
Some horses are genuinely so sensitive that they cannot bear you employing the same pressure points within the mouth indefinitely. The advice I give is logical and has proven over the years to work. The simple solution is that out of all the bits you have tried, re-source the ones that gave you the desired effect and rotate them. Whether you need to change every 3 days, 3 weeks or 3 months; this is manageable. Please also refer to the Section on ‘How to diagnose a mouth problem’.