Question
We have a BIG problem. We started our winter out with 6 Koi, 3 Catfish. We
now have only 2 Koi fish left!!!! The rest have just disappeared! After the first
couple were missing, we suspected a predator (raccoon maybe). So we put a
Koi Dome over the pond. Two more have gone missing. THERE IS NO TRACE
OF THEM AT ALL! We are thinking about putting the remaining two fish in a
fish tank. Do you have any idea of what happened? Any advice would be
appreciated.

Answer
I'm sorry about your fish problem.  How big is the pond?  How big were the fish?  How deep is the pond?  Where do you live (is there any freezing of the water?)?  Could the koi be hiding somewhere?  By Koi Dome, do you mean the underwater castle sort of thing?  

If your pond is shallow, unfrozen, and the koi are small, then, if they are native to your area, I would first suspect a heron and then a raccoon.  If the koi are big, it's not likely a raccoon wouldn't leave a mess if it killed one or more.  Herons can eat larger fish and leave no body parts.

See http://www.fishpondinfo.com/health4.htm#where for a list of why a fish may disappear.

You can net the pond to protect the koi from most predators.  If the koi are larger, or the pond is cold, that's probably a better option than bringing the fish inside.  If the koi are small, and it's not that cold, then you could bring them inside for now.  

I have to keep my ponds netted all the time now (which I hate) thanks to the herons.

Good luck!