Dog collars left for newcomer (7)
I believe the answer is:
settler
'newcomer' is the definition.
(thesaurus)
'dog collars left' is the wordplay.
'dog' becomes 'setter' (setter is a type of dog).
'collars' is an insertion indicator (to collar can mean to apprehend or capture).
'left' becomes 'L' (common abbreviation).
'setter' enclosing 'l' is 'SETTLER'.
'for' acts as a link.
(Other definitions for settler that I've seen before include "Early mover into an area" , "Coloniser - arbitrator" , "New colonist" , "Colonist, pioneer" , "who pays his bills" .)