He's kept busy stocktaking (7)
I believe the answer is:
rustler
'he's kept busy stocktaking' is the definition.
(someone who steals cattle or stock)
This is all the clue.
(Other definitions for rustler that I've seen before include "Horse thief" , "He stole cattle in the old west" , "Cattle thief" , "one whose stock-taking is dishonest" , "lawbreaker" .)