I want to put a back on some shelves. I can’t take out the shelves or work from behind them. My idea is to maneuver a piece of plywood in behind them and glue it to each of the shelves. I will also need to glue a piece of plywood to the top of the piece of plywood I use for the back of the shelves and to the back of the front piece of the shelf unit (hard to explain.) I need a really good strong permanent glue. What glue would be best?