You could try raising the sail a little higher, if you have the room on the forestay, so there is more downward tension on the leach. Add a shackle the the tack of the sail and raise the entire sail that couple of inches. Though that in turn may affect the sail on other points of sail.
But as others have mentioned a snatch block, working as a barber hauler, may also be your answer. But a head
"falling off" is not unusual on a beam reach- its not desirable either, but not unusual.