Underground worker buries dead guard (6)
I believe the answer is:
minder
'guard' is the definition.
'underground worker buries dead' is the wordplay.
'underground worker' becomes 'miner' (I've seen this before**).
'buries' is an insertion indicator.
'dead' becomes 'd'.
'miner' placed around 'd' is 'MINDER'.
(Other definitions for minder that I've seen before include "Bodyguard (colloq.)" , "One looking after" , "baby sitter?" , "One who objects" , "One who looks after (someone or something)" .)