The biggest problem I see is that the part of the board you need to cut off intersects the ground. If you're leaning the board on the ground, you need to someho

The biggest problem I see is that the part of the board you need to cut off intersects the ground. If you're leaning the board on the ground, you need to somehow trace a line parallel to the ground several inches above it. Hopefully you can solve that by using a spare chunk of 2x6 and tracing along that. Similar story for the vertical joint. I don't know if that's what the author meant, though.