Paul I checked out that link to the Aussie forum.
Have a look at the very different ponds. One has a plug point on the pond wall and one pond is made out of corrugated sheet metal of some sorts. I have never seen that.
I only looked at a few pages.

I find it interesting to see what others do.

check it out mate.
http://koi2day.com/forum/index.php?PHPSESSID=0cf88897db8699128fa63be7d545c761&topic=1331.0

To be honest, i would classify those things more as gold fish ponds.

A pond in which koi will be raised needs to be atleast 1m deep and 2m wide and long. That is really the bear minimum in my book. Thats now if you want the koi to be able to grow and to maintain a semi decent body shape.

Theres another discussion on the forum about growth rates...and there are people that achieve good growth in small ponds but those koi usualy lack in the other aspects like body shape and skin quality.