There are many many reasons why horses become barn sour. Simply picking up a crop/spur won't solve your problem. This is a mental issue. What you need to do is teach him that going back to the barn does NOT equal being finished with work. When I work with a barn sour horse I spend a lot of time walking to the barn and trotting back to the ring over and over again (I have the luxury of a very long dirt drive that leads to 3 different arenas), walking in the ring a bit, going back to the barn, back to the arena. On the really stubborn ones I will actually hop off, walk my horse through the barn, then hop back on, and go back to the ring. Sometimes I'll even crosstie them for a few minutes, then bring them back out to work again. There was a horse I had to do that to 4 or 5 times a ride! Sometimes I work in the ring a bit, and then go to the round pen and lunge a bit, then go back to another ring. Basically, I rode them all over the property doing different things... and then I get off well away from the barn, loosen the girth (that's my signal that they're done, not hopping off), and then hand walk back to the barn. When you work in the ring you can do exercises that are more difficult towards the barn, easier away. Don't accept that just because "he's been on the track for 9 years so he'll never calm down". I worked with a horse that was on the track for 11 years and he turned out just lovely. Like I said, this is purely a mental issue and he can get past it. I will warn you he will get upset. Especially if you ride him back to the barn and then try to ride him away. That's when I have used a crop, if a horse tries to put up a fight and needs a little reinforcement that they do in fact need to listen to me when I tell them to go back to the ring. I will also warn you that it's exhausting.
But it can be done. Personally I think barn sourness is a much much easier thing to fix then say, bucking or refusing.
Good luck and keep us updated!