Warm vinegar will generally soften the most stubborn old glue on old furniture. Dipping the parts to be reglued in warm water, and then letting them dry out completely, will help to open up the wood pores and allow the new glue to enter the wood more freely. Warming the parts on top of a heater or in the sun will also help open up the pores of the old wood before regluing.
When building a deck, always nail a thinner member to a thicker member. Hot-dipped zinc-coated nails are a good choice. For more holding power, consider using either ring- or spiral-shanked nails, or go with deck screws. If using screws, it’s best to pre-drill pilot holes.