If the nut is accessible a chisel can be used to tap them around till they loosen, I've had to remove that type of lock nut before for somebody, where it was recessed into an alloy wheel.
I managed to get the spinning outer ring off. I'll have started with chisels, but can't remember if ended up using my die grinder too. Once it was off I used a reverse spiral cut socket smacked onto it, then removed it with an air impact wrench.
This is the sort of socket I used, I don't know how easy you'll find them down under.
If the socket is stuck on the outer ring and spinning, best I could suggest would be welding something to it so it can be removed using a slide hammer.
As an aside, I have the McGard non spin ring type on my TJ. I replaced them with normal nuts when I got a new set of tyres once, as I didn't want to risk damage to the key. When I got it back I tried removing the nuts to torque them all properly and refit the lock nuts. They were so tight I got out a Chinese digital torque gauge I used to have and max torque trying to remove one was over 300 lb.ft at which point the gauge packed in.
My 1/2" air gun wouldn't undo some of them and I had to resort to a 3/4" gun to get those off. Luckily non of the treads were damaged on nuts or studs. I'm sure glad all my nuts are McGard as I think cheaper nuts would have damaged threads at those levels of torque.
