I've seen the Philippine tradition for preserving bamboo (against termites and wood borers) was to soak it in sea (salt) water for 30 days before drying it out for use. Since the fish pen poles had more than that exposure to brackish water, why do you think it rotted out on you? Was it nice and solid when you built the fence or already starting to rot? Curious because I'm considering building a bamboo house but don't want to put the effort in if it'll only last a few years. Some videos contend 30-50 years is possible if the bamboo is properly preserved -- which is my hope.
I'm not an expert, just going by my Filipino brother-in-law's suggestions and advice. The bamboo from the fish pen was solid at the time and we were told it would be good for termites. The one thing we didn't do is cap the posts, so that might be a suggestion for longer life. We had a neighbor that got larger fresh timber bamboo a few years ago for a house build brought in by truck and we watched them soak in the sea for a few weeks. The house never got built, the bamboo was stacked, and is now no good. Maybe varnish is the trick? Who knows? For me, a $40 fence is a pretty good deal even if I have to replace it every few years. Good luck 👍
