As Dr. Strasser has pointed out, a constantly maintained wild horse trim, coupled with plenty of exercise and constant freedom to move, is your best line of defense against laminitis. She finds that all foundered horses have high heels and some degree of heel contraction. Trimming as she advocates will spread the heels and enhance circulation enough to provide more reserve circulation to better withstand laminitis triggers. Drinking too much water when hot is another way.
Obesity greatly increases the probability of founder.
Gorging on grain can do it. Gorging on the new spring grass is another way. Bedding on black walnut shavings is an example of a toxic trigger. Over-use of steroids is another systemic trigger. Many of these can be avoided.