I'm making a large cake. Its a 11x15 wild hog cake like this one.
http://cakecentral.com/modules.php?name=gallery&file=displayimage&pid=1311311
What can I made the cake board out of?

I would try and cover the board with fondant and keep it in earthy tones, either grassy or dirt and keep the fondant loose and maybe you can scatter dark chocolate cookie crumbs to make it look like the ground. Just a thought. Good luck.

I use foam board that I buy at Michaels or AC Moore. They are very sturdy, yet not heavy.

Ops Im sorry I guess I understood you wanted ideas on how to decorate your cake board. Silly me. I use foam board and if my cake is extra heavy i double it and then cover the board. You can also get precut pieces of plywood from the lumber store and cover them, they make for a very sturdy board.

thanks!

I always mdf, plywood, melamine board to my boards. I clean it, let it dry, wrap it with plastic wrap and fondant on top. It is surely sturdy and will never let you down.