It’s a great idea to teach your horse to rebalance when you do the “sit up (but not down)” action, i.e. when you bring your shoulders back and engage the horse with your legs but keep the seat really light.
This makes a HUGE difference xc, once horses really understand it you can keep coming in a rhythm with, ideally, no fighting in front of the fence. Top riders do it automatically, in fact so instinctively that I don’t think they necessarily realise they are doing it… not many teach it, in my experience!
Of course it needs practising a lot at home, and you can only gradually make it happen closer and closer to the fence… e.g. I’d say ask the first time say 30 strides away, and then if nothing happens you have plenty of time to ask again and make it clear to the horse what you are asking for!
Gradually you can hone the aid until the horse rebalances immediately as you bring your shoulders up, as you near the fence.
Of course the type of fence you are approaching hugely affects how strong the aid should be, have a look at my notes on the Yogi Breisner lecture for more info on that.