Commander, the fool, maintaining police work is to take place (4,2,4)
I believe the answer is:
come to pass
Here is my best explanation:
'is to take place' is the definition.
(I've seen this before)
'commander the fool maintaining police work' is the subsidiary indication.
'commander' becomes 'co'.
'the fool' becomes 'ass' (ass is a kind of fool).
'maintaining' means one lot of letters goes inside another.
'police' becomes 'met' (I've seen this in other clues).
'work' becomes 'op' (common abbreviation for 'opus'**).
'coass' placed around 'metop' is 'cometopass'.
(Other definitions for come to pass that I've seen before include "Take place", "reach mountain road", "Happen", "Short military stick" and "Biblically happen".)