Plain Old Wood Glue is Best
Wood Glue Can Last for Years
Use Waterproof Glue for Outdoor Projects
If your carpentry project might get wet, use glue that stands up to water. Glues labeled 'water resistant' are fine for things that'll only get wet occasionally. For most outdoor projects, however, choose 'waterproof' glue, which comes in both PVA and polyurethane formulas. Both types are plenty strong and stand up to the weather, but polyurethane glue has the added benefit of being able to bond materials like stone, metal and glass. It's messy stuff, though, so wear gloves while using it.