Cruciverbalist's job getting harder (7)
I believe the answer is:
setting
I believe this clue is a double definition.
'cruciverbalist's job' is the first definition.
(a crossword setter is a type of cruciverbalist)
'getting harder' is the second definition.
(Other definitions for setting that I've seen before include "Surroundings of a place" , "Metal holding a gem" , "Mount for gem" , "Writing puzzles, perhaps" , "Gem''s mounting - stage scenery" .)