The dark straight line across the middle of the board is the first scoring line. All dice must completely cross that line. If a die does not completely cross the line, it is removed from the board and counts as a turn.
Oops I've been playing it wrong as we left those die on the board. Gonna start playing it correctly. Not sure how I missed that rule. I guess it makes since as it doesn't allow for blatant defense perimeters to be set up.