My 120V walkway lights use UF cable (not in conduit). Am concerned the cable may be cut during an upcoming replacement of the concrete walkway. What is the proper way to protect any underground splices that may be required?

A proper UF splice kit, like those made by 3M or GB.

You can also spray paint the entire branch circuit so that the workers will know where the lines are.

If you ask nicely, you may be able to get Miss Utility (that's what the service is called here in VA.)