Objective: How to make a grocery list for the fridge?

Which of the following solutions is more sound in terms of naive physics reasoning?

Choices:
a). Purchase a small black board and glue a magnet to the back, run a small piece of wood glued to the bottom of the black board and place chalk on it, then place the black board on the fridge.
b). Purchase a small black board and glue wood to the back, run a small magnet glued to the bottom of the black board and place chalk on it, then place the black board on the fridge.
a).