Night hunters point to possums and raccoons. I have not had bird problems, so I know little about that, but maybe owls hunt at night. Here is what I suggest:
1) If your sides are not steep and there is room for the predators to wade, put in a koi cave in a deep section. You can either purchase them over the net or build one with planters, milk crates, etc. Basically, just create a shelter for the fish to hide in when spooked.
2) Bait a Havahart trap and relocate the buggers some place far, far away.
3) Install an electric fence around the pond.
4) Keep the dogs out at night.