Caution to protect sappers in maze (6)
I believe the answer is:
warren
'maze' is the definition.
(I have seen 'Maze of passages ' mean 'warren' so perhaps 'maze' could also mean 'warren')
'caution to protect sappers' is the wordplay.
'caution' becomes 'warn' (I've seen this before).
'to protect' indicates putting letters inside (inserted letters are held or protected).
'sappers' becomes 'RE' (Royal Engineers).
'warn' enclosing 're' is 'WARREN'.
'in' is the link.
(Other definitions for warren that I've seen before include "Rabbit colony" , "Film star Beatty is down with the rabbits" , "Network of tunnels created by rabbits" , "Home to rabbits" , "boy" .)