Geophysical survey techniques provide a cost effective and direct method for locating anomalous features and zones of weakness within sea defences and man-made structures located at the sea-land interface. Combined with simple nondestructive testing (NDT) techniques the presence of cavities, zones of weakness and salt water ingression may be detected. This paper reviews available techniques and illustrates the application of several techniques to particular structural situations such as the detection of voids and material changes beneath sea defences and promenades and the monitoring of zones of weakness in a stone pier. With the recent advances in electronics, improved instrumentation is becoming available which, with the developments in computer based interpretation software, is leading to several geophysical techniques being far more applicable to site investigation prior to the construction of new structures and the long term monitoring of existing structures for possible in-situ defects.