The stomach behind the behaviour
A horse's stomach produces acid around the clock, whether or not there is food in it, and forage is the buffer: a grazing horse chews for hours, and all that chewing produces the saliva that calms acid, while the mat of fibre in the stomach stops acid splashing onto its unprotected upper lining. That is why ulcer-prone horses so often unravel on the same pattern - long hours with an empty stomach, large infrequent concentrate meals, hard work on an empty gut, and a routine full of disruption. Management changes work by reversing that pattern piece by piece, and for a horse with a known history they support the vet's plan rather than replacing it.
Forage first, and nearly always available
The single biggest lever is forage access: hay or grazing in front of him as close to continuously as his waistline allows, so the stomach is rarely empty for long. Where weight is a concern, use small-holed nets or slow feeders to stretch a measured ration across more hours instead of cutting the hours it covers. Give a small net of hay before travelling and before work, so acid has fibre to sit on during the very activities that splash it around. Avoid gaps of more than a few hours without forage, and make sure water is always available - a horse who drinks well buffers better than one who does not.
Rethinking hard feed and the shape of the day
Concentrate feed works against an ulcer-prone stomach when it arrives in two large meals, so split the same ration into three or four small ones, and favour fibre-based feeds over large starchy buckets, discussing the details with your vet or feed adviser where his condition demands it. Then look at the day itself: long, settled turnout with companions he gets on with, a routine that runs at predictable times, and calm, unhurried handling all lower the background tension that tracks with gut flare-ups. Even stable design plays a part - a horse who can see other horses over the door frets less than one shut away alone with nothing to watch.
Tracking which changes actually help him
Because no two ulcer-prone horses respond identically, keep score. Note his appetite, his girthiness when tacked up, his willingness under saddle and his droppings against the changes you make - forage timing, turnout, feed splits - over a few weeks, and the notes will show you which changes genuinely settled him and which were neutral. Take that record to your vet reviews, because it turns 'he seems better' into evidence the plan can be adjusted on. And if he loses weight, goes off his feed, shows signs of colic or his behaviour deteriorates, that is the vet's call to make promptly, whatever the management is doing. KinsLe's Pet Passport keeps those management notes filed alongside his vet history, so the whole story of what helped is in one packet at every appointment.