I google searched 'pond fencing requirements' just the other day, and the first link that came up was this link
http://www.ccc.govt.nz/QuickAnswers/Bui ... /F1709.asp
Where it says
"Under the Fencing of Swimming Pools Act 1987, a pond is considered to be a swimming pool, and must be fenced in accordance with that Act if:
(a) "...the maximum depth of the water exceeds 400mm" Section 5(b),
and
(b) it is "... used in association with any house, home unit, apartment building, school, hospital, hotel, motel, camping ground, or other similar premises" Section 5 © (i).
To avoid the need for a fence in the above situation, it is suggested that an overflow be constructed that prevents the water ever being more than 400mm deep (eg, after rain)."
That one is only for CHCH but id say it should be the same everywhere else...