There's a glue out there for sticking nearly anything to anything else, but none of them work well underwater. While this might not be a problem for most people, a good underwater adhesive would be helpful in a variety of niche circumstances. Fortunately, a good underwater adhesive does exist: it's used to stick mollusks to rocks.
Mollusks often spend their whole lives stuck to a single rock, and not even the strongest waves can knock them off. This is due to the special adhesive the animal manufactures, which contains the amino acid DOPA. A group of Purdue researchers set out to copy the mollusk's water-resistant adhesive strength by using that amino acid in their own work.
The researchers synthesized an artificial version of the adhesive, including DOPA and other mollusk proteins to see if they would improve the adhesive strength underwater. To their surprise, not only did the artificial adhesive work underwater, but it was also 17 times stronger than the mollusk version. Such a powerful adhesive will likely end up in construction projects and repairs as an alternative to underwater welding.