Prior research has demonstrated that global positioning system (GPS) spoofing attacks on phasor measurement units (PMUs) can cripple power system operation. This paper provides an experimental evidence of the feasibility of such an attack using commonly available digital radios known as software defined radio (SDR). It also introduces a novel countermeasure against such attacks using GPS signal redundancy and low power long range (LoRa) spread spectrum modulation technique. The proposed approach checks the integrity of the GPS signal at remote locations and compares the data with the PMUs current output. This countermeasure is a ready-to-deploy system that can provide an instant solution to the GPS spoofing detection problem for PMUs.