Well, it's summer time. That means every animal is roaming about at night. A few nights ago I heard a loud splash and took a flashlight into the backyard to see what happened. There was water on the ground around the barrel. Some of the lily leaves were torn at the stems. My guess was that it was a raccoon, possum, or skunk. Then last night I heard the neighbor's two dogs barking while some other animal snarled and hissed.
What's my point? I had to build a perimeter around the goldfish barrel. It's not the prettiest, but it was cheap and I think it will work.