1
general::
Assume responsibility, especially in another's absence; also, maintain a secure position. For example, Harry did a good job of holding the fort until his boss recovered, or Can you hold the fort in the kitchen? This expression has been traced to an order given by General William Tecumseh Sherman in 1864, which was repeated as "Hold the fort [against the enemy at Allatoona] at all costs, for I am coming."
American Heritage Idioms
2
general::
Phrase(s): hold the fort
Fig. to take care of a place while someone who is usually there is gone, such as a store or one’s home. (From western movies.) • I’m going next door to visit Mrs. Jones. You stay here and hold the fort. • You should open the store at eight o’clock and hold the fort until I get there at ten.
McGrawhill's American Idioms And Phrasal Verbs