9 Marking The outside For The Cut

So I measured down 3/4" on the outside and marked where to cut the wall. I didn't take a picture of the cutting process; it wasn't pretty and it took a while. I scored the wood as deeply as I could from the outside with my utility knife and then used my little craft saw to try to cut through it, an inch at a time, carefully breaking it off as I went. I'm sure there's a better way to do this, but I don't know how. It worked, anyway.