Resorcinol (sp) is waterproof and works very well for a permanent joint. I've used it extensively in teak woodworking.
DAP WELDWOOD Resorcinol Waterproof Glue is a high performance, two component adhesive designed to provide the strongest, most durable bonds in severe service application. Once cured, Resorcinol withstands continuous salt or fresh water immersion, outdoor exposure, tropical or sub zero temperatures.
DAP WELDWOOD Waterproof Resorcinol Glue is designed to laminate structural wood beams, also provides durable bonds on a variety of porous and semi- porous materials such as wood, particleboard, leather, cork, concrete (cured) and crockery (unglazed).