So my horse has this issue of hitting 3rd barrel when it's on the fence. Think rodeo pen close to the fence. Like she will shoulder half way there and just run it over.  Other runs indoors when it's not right on the fence she is fine. To be honest I think shes scared of running into the fence because she's honest when there is more room.  Has anyone had a horse like this? This isn't a matter of "push past it,  look at the fence, don't drop early" this horse just consistently does it in those set ups. Any ideas how to get over it? Shadow roll? Running her to the fence in exhibitions? 

To add this is not a soundness issue

Well,, that needs to be on your list or practice drills. Like everything else start at a walk. Straight to fence. Don't let her turn off either direction. Go to fence, back a step or two and rest. When comfortable with that, move up a gait. 

Do you have a video you can post?

If your horse is hitting the 3rd barrel when it's close to the fence, then you need to look at what YOU are doing to cause it. Horses don't enjoy slamming their body into a barrel. If you are subconsciously cueing her too soon, she's going to hit it. If she has learned over time that that  is what you want her to do (cue too soon and turn too son), she is going to hit it because it's a bad habit and you've taught her that.

While horses have most of the control during the run, she does still have to listen to you if you ask her to "wait" one more step or you have to make a small adjustment.

No matter what, you have to go back to slow work. Teach her to hit the pocket perfectly, each and every time. Work on your horsemanship too. Work on getting her even more soft and supple to your legs, seat and hands.

Another thing - when she does to turn too soon .... what are you trying to do to stop her? Are you making the classic mistake of allowing your inside hand to cross the plane of her mane?

Again, a video is going to be much more helpful to determine what is going on. But most of the time, it's something the rider is doing to cause it.

If you can get in the arena ahead of time, I like to lope circles with one side of the circle right up against the wall, I don't like the extra stress of involving a barrel, just nice easy circles with one side close to the wall.  Lots of praise, very relaxed, I think it takes thier (and your) focus off the wall and on communication.   Don't look at the wall, just ride to your spots on the ground as close as you can get without hitting it.

I had this same issue with my mare.  Joy Wargo futuritied her for me so I asked her what I should do.  She said to get 2 exhibitions and lope through.  I did this and it worked.  On the first exh., I smooch her all the way to the fence on the turns.  Second exh., I go back to normal.  It is a pain having to get there early to do exhibitions, but it fixed her.  I hope one day my mare matures enough we can stop this.

Coming from a cow horse/reiner perspective, have you tried fencing him?

A lot of people think fencing is about teaching or forcing the stop but it's actually about teaching the horse to run all the way to the fence with confidence and not scotching. 

Maybe take the barrels out of the equation, start slow and trot him all the way to the fence, let the fence stop him, keep him between your feet and hands. Let him rest and pet him. Work him up to to loping him all the way to the fence then running him. Show him he can run all the way down with out crashing into the wall.

I feel your pain. I had a futurity horse that was TERRIFIED of ... a lot. We did expos once (3-4 of them) Never made it all the way up to the third barrel LOL. Thank fully in her run she kept her Sh*t together and worked well.

In that case, the trick was to stop doing expos. Then he didn't know where the monsters were. 

If I were you, I'd start doing a lot of fence work. If she is a seasoned horse, You may want to think about a good spank. You are scarier than whatever is on that fence. Tough vice to crack.

Also have seen a drill going around the outside of arena on the "incorrect" lead. So if you are loping clockwise, you'd be on the left lead. Turn into the corner (left), come around and continue clockwise on the left lead. Should get them working a corner and less scared of boogeymen. Teach to turn by a fence. 

Barrel Horse News just posted an article with Sharin Hall about doing wall to wall work. It would be worth a read for you, I think!

https://barrelhorsenews.com/barrel-racing-articles/training-40510/sharin-halls-two-wall-barrel-racing-drill/