Oh well, had no heron four days after I installed the fishing wire properly, probably due to rain, so I didn't know how effective it was.
It came back yesterday. Tried to get past, and couldn't. It walked around for 20 mins, trying to find a way in, but couldn't, so it flew off. I was happy that the thing was working.
Woke up today to find it had eaten another fish. The video reveals that it ducked down and managed to walk under the wire (around 8 inches from the ground). Here's the fragment where it gets it's meal. Once it spotted the fish it flew accross the pond and picked up the fish mid-flight. As it tried to exit towards the side it flew straight into the wire, struggled a bit, but freed itsself and devoured the rest of the fish.
http://zone-mr.ath.cx/content/photos/house/Heron2.wmv
Grrrr... going to try and move the wire lower, and closer to the pond, and I'll also install an electric fence around the pond tonight. If that doesn't work I don't know what will.