What must a person do to protect himself from sorcery, given that he does not know its whereabouts after his son threw it away?

To be protected from magic (sihr), one must adhere to the piety of Allah Almighty, maintain the morning and evening remembrances (adhkar), and increase in supplication (dua). As for what is believed to be magic, it should be buried, as the Messenger of Allah, peace and blessings be upon him, did when he was afflicted by magic. One should not succumb to delusions, but rather rely upon Allah Almighty.