Maybe go down a level? My horse is 21 and used to jump 3ft, now we only do 2'3-2'6 , he's been sound ever since !
Try wrapping his leg in a standing wrap after hard work, and maybe apply a liniment or poultice (explore proequinegrooms.com). A ligament supplement (check out smartpak.com) could also help him. He should also be checked by a vet!
Thanks Katie, he's only 11 and only seems to happen if he's pushed to his very very limits which is what's needed for hunter trials.
If it cannot be managed, yes. Or retired.