In the bible David hit Goalith in the head with a rock What did David do to ensure that goalith was dead?

1 Samuel 17:50, 51 - So David prevailed over the Philistine with a sling and a stone, and struck the Philistine and killed him. But there was no sWord in the hand of David. Therefore David ran and stood over the Philistine, took his sWord and drew it out of its sheath and killed him, and cut off his head with it. And when the Philistines saw that their champion was dead, they fled. [NKJV]