I would recommend a series of ultra small, discrete transmitter-repeater type tech be employed. A small device that can be placed “sticky” on the fly, something that is not easily noticed -that can communicate within a small radius, line of sight or bounce around walls.
This device should use the best battery tech available for at least a few days of comms.
Two squad members near the back would be tasked with placing these devices along their *course.
*Two offers redundancy.
In addition some sort of “breadcrumbs” could lead a squad back to the last known position of the last transmitter /repeater. This could be high tech or something that only can be seen with uv glasses for example. Taking a moment if possible to place these markers - with a known “signature” could also help a squad if the trail has been interfered with. One squad member could add this to their duties.
In exceptional circumstances, an agreed pattern of blowing up charges, would give ground command something they could measure, use those blasts as a signal to approximate your location and any message that was pre agreed upon in the number of blasts, then send the boring tunnel rescue team down below.