When I'm riding my horse and he is absolutely frozen about to explode, I let him get a good look at whatever's bugging him, then urge him forward, and walk him by it 209830428 times till he's calmed down about it significantly. Then I will stop him in front of the area, and feed him a sugar cube [on his back, yes he has mastered the art of taking a sugar cube from my hand from his back, and seeing as how they dissolve there's no interference with the bit.] This is my way of telling him, see that's not so scary, here's a sugar cube for trusting me! Then, when I'm off his back and cooling him down I will stand with him in that area, let him touch the scary thing with his nose, and tell him he's a good boy.
I remember once I was riding and he was absolutely horrified, frozen, because of an orange traffic cone in the corner of the arena. I walked him by it over and over, then trotted and cantered by it till he was significantly calmed down. Afterwards I let him touch it with his nose, then proceeded to pick it up and pet his nose with it. He got the jist of what I was trying to say :]