A method for monitoring depth of a cave front in a cave-type mine. The method includes: providing a stationary reader device and mobile marker devices, each of the marker devices adapted to (i) emit an electromagnetic signal, (ii) detect strength of the signal emitted by another of the marker devices, and (iii) wirelessly transmit information related to the detected signal via the other marker devices to the stationary reader device; drilling a hole into a rock region of a mine, installing the mobile marker devices at sequential known depths within the hole; monitoring the reader device to detect a decrease in the strength of a signal emitted by a first marker device by a second marker device; and in response to a decrease being detected by the second marker device, inferring the depth of the cave front to be between the known depths of the first and second marker devices.