For me it is the raccoon, hands down - but your experience is worse.
I have raccoon visits about five nights a week now. They can't do too much damage (except for getting the dogs, and hence me, to run outside at 3 am) but they always play in the filter, and dislodge the slate of the waterfall, often causing the pond to start draining itself. I feel guilty adding 500 gallons weekly when we are being begged to save water.
I have now had my waterfall turned off for awhile, and run it only on sunny weekend afternoons when I am physically pondside. Have no place to rig a fido fence, but boy, when I do get even with these critters, it is not going to be pretty.
Grumbling away,
Mike
Adding a photo of the scrubbies that were liberated in a recent attack.