Abstract: A security tag used with an electronic article surveillance system for detecting the presence of the tag within a surveilled area utilizing electromagnetic energy at a frequency within a predetermined detection frequency range includes a dielectric substrate having first and second opposing principle surfaces, a peripheral outer edge, and a resonant circuit capable of resonating at a frequency within the predetermined detection frequency range. The security tag also includes a guard member, in one embodiment a discontinuous conductive member, effectively electrically isolated from the resonant circuit, extending along at least a portion of the peripheral outer edge of the substrate for surrounding at least a portion of the resonant circuit. The guard member electrically isolates the resonant circuit to facilitate testing of the resonant circuit during an early stage of the manufacturing process when the resonant circuit is in web form.