how to protect fish in an outdoors fishtank against raccoons?

Hi,

My parents have two fishtanks too large to be placed inside the house,
so they set them up in the backyard. In them they had some 20 different
fish, big and small, that they took care of everyday. But this morning
when they went out to the yard, they found the fishtanks ransacked,
with the fish gone, their body parts scattered on the ground. It
appeared that some wild animal snuck in in the middle of the night, forced
its way through the surrounding flower pots, took off the covering glass on
top of the tanks, and had quite a feast. Since some of these fish my
parents have had for three years, needless to say they were really
heart-broken when they saw the massacre in the morning.

This is not the first time it happened. In the past, there were a
couple of incidents some wild animal (our guess is raccoons) came in at
night, eating our fish, leaving a mess behind. Learning the lesson the
hard way, my parents have put up added defense against such intrusions,
short of killing the intruders with poision (frankly now I'm very tempted
by that idea). But last night topped them all, with but one of the 20
fish barely alive.

So my question is if anybody could suggest a way of preventing this
from happening again. I know people here in New Jersey, bothered by deer
entering their yard, put up electric fences. I wonder if there's anything
like that for fishtanks as well. Also, since my parents live in the
outskirts of Los Angeles (more inland area), their backyard facing the
foot of the hill, does anybody have any idea what kind of animal could be
doing all this damage? Is a raccoon capable of such things? Do they eat
fish?

If you know of another newsgroup that more directly deals with this
kind of questions, please let me know. Thanks in advance.

-Ed