I really like this and think it would be a sick tattoo on the inner wrist. The word valknut is a neologism: it is formed in modern times through combination of ON valr, ‘the dead’ or ‘the slain’ and knut, ‘knot’.
"Sparta has no walls because you, her warriors, are her walls. Sparta’s boundaries are undefined because these your spear-points define her borders. So when the Barbarians come, let them find nothing but death on the frontiers of Sparta!