I am still very new to decorating cakes, but my question is this. After a cake sits on a white cake board, say overnight, the next day it looks like the cake leaked out the side.

I need to use the white board, and it needs to be a little bit bigger than the cake. It's for a smash cake. How do I avoid this happening?

If using white top corrugated cake circles, you can cover them with Wilton white fanci foil to prevent grease stains or buy greaseproof wax coated circles. To make the presentation board look more professional without the raw corrugated edges showing, covering it is a great option.

It's cheaper to buy white freezer wrap in the foil section of the grocery store. Just make sure the shiny side is out. It's great. I put my cakes directly on it to decorate. Wipes clean!
Put a ribbon around the sides and you've got a nice presentation.