Used Back on Track neck cover. Size Large. Clips had been removed so that it would go on under my horses winter neck cover (they were not placed well to clip on to the blanket anyway). Even then, it didn't work well and kept shifting. Only used 3 times.
I have the clips so they can be re-attached, but if you do so, the neck cover cannot be left on the horse unattended as they would dig in if the horse laid down. Better to make your own velcro attachments for it instead.