I am not exactly sure what the porcupine structure is (but can imagine), but this is something inexpensive I used in my pond. 5-gallon bucket, 1 bag of concrete, paddle bit, and leftover irrigation poly tube. Ended up with 3 of them in the pond. They do get pretty heavy and tricky to place. Probably get away with just adding enough concrete to lock in the poly tubing and call it good.
I found this online and are building 10 of them. They are made from plastic barrels cut in half. I also cut out most of the ends so that fish could swim underneath as well. Each one has 20 five foot pieces of 1/2" irrigation tubing looped through the holes I drilled. Total cost: Barrels were free and tubing costs $35.98 per 500' roll. I used two rolls so I have less than $80 in the entire project.
We was throwing them away at work. So I snatched them up. Figured I'd make some kinda cover for fish with them. I have used some of the full barrels before. These our underwater in the 2 -5 foot range.
Also going 2 (maybe) plant a lilly or 2 or maybe lotus. Not for sure.