The phrase "holed up" is used to describe a situation when something or someone is secured in a safe and often hidden place. In this context, when we say "A ship was holed up," it refers to a ship being sheltered or in a safe, protected place (such as harbor). "Halting on" and "Heed at" do not fit the context, and "Hauled at" is not a commonly used phrase in such a situation.
Thus, the correct phrase is (a) Holed up.