Well over a year has passed and we've only had 2 minor cattle incursions since installing the electric fence, one of which was following a heavy story and a tree collapsing the fence and the other was embarrassingly due to fence maintenance that I missed, so thanks again for your help and advice with this.
My next phase, and it's going to be a big one, is to redo the boundary at the edge of the woods which is in a terrible state but didn't want to repair it all and have half tonne wrecking machines trying to climb over it and destroy it. I'm now confident that is approach will work and I can continue on from the last section using the same energiser etc.