digging problem

My monster with a empty falls through the ground because the cubes end that are underneath it.Because they are supposed to be boxes underneath when it digs.When it digs they are no boxes underneath the grass box.I am using a parent to nearest property script.How would i prevent this?Press w to go forwards and use the mouse to turn.Here is the blend.

Attachments

blockWorldEasyDemo2.blend (887 KB)