Check what rustlers do (4,5)
I believe the answer is:
take stock
'check' is the definition.
(thesaurus)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for take stock that I've seen before include "shop-lift" , "See how the land lies" , "as shoplifters do" , "How to start preparing soup" , "Make an appraisal" .)