A locking fire hydrant includes a fire hydrant body having an internal channel extending between a main cap recess and an auxiliary cap recess defined therein. A plunger assembly including first and second plungers is disposed within the internal channel. The first plunger is disposed such that an end thereof is capable of extending into a main cap recess and the second plunger is disposed such that an end thereof is capable of extending into an auxiliary cap recess. When the second plunger is actuated by mounting a locking cap on the fire hydrant body, one of the ratchet teeth provided on the back side of the auxiliary cap engages the second plunger to prevent the auxiliary cap from being removed from the fire hydrant body. A locking cap, an opening tool, and methods of securing an auxiliary cap to a fire hydrant also are described.