In 1807, American foreign trade was diminished when Jefferson implemented the Embargo Act in response to British threats to U.S. shipping. The same year, Jefferson signed the Act Prohibiting Importation of Slaves. After retiring from public office, he founded the University of Virginia. His father Peter Jefferson was a planter and surveyor who died when Jefferson was fourteen; his mother was Jane Randolph. Peter Jefferson moved his family to Tuckahoe Plantation in 1745 upon the death of William Randolph, the plantation's owner and Jefferson's friend, who in his will had named him guardian of his children. 'Shortly after Jefferson had died, attendants found a gold locket on a chain around his neck, where it had rested for more than 40 years, containing a small faded blue ribbon which tied a lock of his wife Martha's brown hair.Jefferson's remains were buried at Monticello, under an epitaph that he wrote: