How to get my QH on the outside track in the arena!!?

Okay I've been working LOTS on my geldings overall posture in the arena, he has built up a lot of muscle over the last year and lost a lot of fat so he's looking a very good weight right now. He's been going very well in the arena (I do dressage by the way). He is going round nicely and moving forward and collected very well. He tends to lean into the bit, being a QH and not really built for dressage but I work the bit a tiny bit in his mouth and use a tiny bit of leg and he picks himself up again. When he's going good I don't work the bit at all I keep my hands very still. I do carry a dressage whip because occasionally he'll ignore my leg and I'll work the bit but still need some assistance so I give him a tickle with the whip.

Anyway, the outside track around the letter R is a big issue, there are horses (mares) in the paddock next to the arena so it can be hard to keep him focused but he's getting a lot better. Anyway he once got shocked by the electric fence on the other side and now he won't go near the letter R. I don't know if this is just a problem at home or if he'd be the same at a comp (I don't think he would but still). I try my best to stay still and not react to him, but as soon as we get near R he leans off of the track and will go back on it after. I use so much inside leg it's ridiculous, if I use my reins he'll just turn his head and his body will stay inside, does anyone have any tips for this?