The tax office documentation does clearly state that replacing a fence is capital in nature.
I'm not really sure whether your argument about "replacing it is repairing it" would really hold much water. There is really little difference between my fence which had fallen down due to rotten posts and had to be "replaced to be repaired" and yours which had fallen down due to a storm.
The way I had it explained to me was that if you could essentially use the existing materials and reconstruct the original structure (ie. bang in a few nails, straighten a few posts), then it could be classed as a repair. Replacing any item (fencing or new posts) essentially makes it a new item, and hence capital in nature.
I'd be interested to hear anyone elses opinion on this.
I went through this same type of circumstance a couple of years ago with a masonry block fence that had come down during a cyclone in NQ. The insurance didn't cover it because it was not attached to the dwelling and even though it was replaced with a fence of lesser quality (arc-mesh) I had to claim it as a capital expense. I didn't really believe my accountant but after my own investigation found her to be correct.