I am leasing a horse that is the exact same way but is afraid of just about everything not even just whips. I found the best thing to do was to just have whips, empty grain bags (whatever the horse is afraid of) in your riding arena. I started off lunging him with a whip next to my feet. Then after he was comfortable with that i would hold it in my hand (NOT USING IT) then i would start to rub it on his legs and just slowly move forward as he felt comfortable. DO NOT try to rush this process the faster you try to go the worse your horses experience will be. Also, make sure to not have the scary item with you every time you work your horse because then your horse will start to associate work with the scary item and will not longer want to work. Best of luck to you!