Wood needs to be protected otherwise it will split and crack. Here are a few good ways to seal your board.
Step 1: Water based polyurethane: paint it on and let it dry.
Leaves a durable clear finish on the board like its coated in plastic. 1-2 coats should be enough.
Step 2: Linseed oil: a natural way to finish the board that brings out the colors in the wood.
Requires many coats for a durable finish. At least 2-3 coats with a day to dry between each, more is better. Re-oil the board anytime it starts to look dry. Be very careful when working with raw linseed oil since it is highly flammable and can spontaneous combust if the brushes or rags are not disposed of properly.
Step 3: Paint: any kind of paint will help protect the board; house paint, spray paint, or enamel.
Paint two coats to make sure you’ve got a good seal. If water soaks under the paint it will bubble and peel.