Tamper resistant locking device for fire hydrant

A fire hydrant locking device, comprising:

• a collar assembly, having a pair of arcuate arms pivotally disposed and dimensioned to encircle a barrel of a fire hydrant, a tab protruding from ends of the arcuate arms, the tab each having at least one slot that is coaxially aligned with the collar assembly in a closed position;
• and
• a retainer leg having an aperture defined in a top end thereof, the aperture having a geometry that is dimensioned to receive a corresponding geometry of an operating nut of the fire hydrant, a bottom end substantially orthogonal to the top end, such that with the aperture secured to the operating nut of the fire hydrant, the bottom end is oriented to be received in the at least one coaxially aligned slot of the collar assembly, wherein the aperture geometry engages with the corresponding geometry of the operating nut to prevent rotation of the operating nut.