Praise be to Allah.
Believing that the dead can guard items that are placed at their tombs is blatant kufr and shirk, associating others with Allaah in His Lordship (Ruboobiyyah). Whoever dies believing this deserves to spend eternity in Hell. Placing items that one wants to keep safe and other things at tombs to be guarded or to receive barakah (blessings) – all of these actions are not permitted at all. And Allaah knows best.
And Allaah is the Source of strength. May Allaah bless our Prophet Muhammad and his family and companions, and grant them peace.