Barryian asked: "What are your fish afraid of that they need to hide? lol ... ok, just a joke!"
I have lived in the Western NC mountains for 2 years. Have seen many black bears, but they never came to my pond, that I know of. At least the fish had not acted scared and gone to the bottom for any length of time indicating this. So, when I looked at my pond last week and saw a big ole' bear pawing at the leaf net and splashing water out of the pond I figured I'd better do something. Wish I'd gotten a picture, but I was quicker to yell at him to leave than pick up my phone and shoot pix.
So that's why I'm hoping to give them some more protection. I was hoping for something heavier than PVC and was looking at clay chimney flue pieces. But a 2 ft length of 24" square clay flue pipe costs $150! A little more than my retirement budget will allow. So 12" PVC sewer pipe it will have to be. At $39 for an 8 ft piece it's a bargain!