Image distortion caused by field inhomogeneity and instability is a major limitation for open MRI systems. Magnetic Field Monitoring (MFM) is a well-documented approach to characterise and thus compensate for these effects using an array of NMR probes. Here a novel NMR probe with a secondary coil is presented, which is designed to protect the pre-amplifier during transmission of a uniform B1 field. Preliminary data has verified this result and temporal variations of the B0 field have been observed. This approach will be developed with multiple probes to measure and compensate for the spatio-temporal response of the system.