Problems with your garden pond

2. My Goldfish, Carp or other fish are getting eaten by herons

This, to be sure, is an annoying problem. Herons are beady-eyed creatures and they can spot a fish from a great height. All you need is one of these visitors on a regular basis and you can find your whole pond cleaned out. A bit like curing warts, there have been various solutions, some more succesful than others, offered up over the years to stop fish-loss by heron. Here are a few ideas.

Get yourself a fake plastic heron. They're territorial creatures and if they think another heron's already there, they're unlikely to come and encroach on their territory. Of course, this will only work for a while. Herons aren't entirely stupid and after a while they'll start to smell a rat. Try moving your plastic heron around to prolong its effectiveness.
Get some heron netting. Ok, it doesn't look great, but we're in a desperate position here. All your prize koi are getting eaten - who cares how your pond looks!
You could always go down the electric fence route. Install one of these around your pond and the heron will certainly get a shock as it steps forward for its usual fish supper. Obviously care needs to be taken when messing around with stuff like electricity. Bear in mind too that herons are a protected species so don't go too far!
As herons tend to stalk from the edges of bodies of water, you could always make their life a bit more difficult by growing plants around the edges of the pond. Obviously this has the drawback of obscuring your pond from clear view. It's another compromise unfortunately, and depends on how much you value those fish.
Make noise around your pond. Lets dogs or kids play around it and they'll be sure to scare the herons off (they're pretty shy creatures after all). Alternatively you might want to consider some sort of sensor-activated alarm system if you're really desperate.