I have used this to stick aquatic bits and pieces together.
https://www.jbl.de/en/products/detail/8058/jbl-proharu-universal
Works better than aquatic silicone on things like rocks and wood, as does actually appear to stick to the items, unlike silicone in my experience, where the water eventually creeps underneath the silicone, especially wood, and the silicone loses its bond. There are very few things that normal silicone actually bonds to, normally some "harder" plastics and very handily glass. This JBL stuff is certainly better. Looks to be just a "superior" neutral cure silicone, giving off methanol rather than standard acetoxy silicone that gives off acetic acid.
It also appears to last longer once opened, unlike my aquatic silicone where I found it had all set solid in the tube after only a month or two after opening.
Also remember 30-40 years ago (when I was a kid
), in fish keeping, people sealed their tanks & glued rocks and wood, using the only available silicones, no B&Q in those days, just local "hardware store". These silicone generally contained a fungicide and certainly gave off acetic acid when curing, but I don't remember fish wipe outs due to poisoning .
.