A barrier, worker being stubborn (7)
I believe the answer is:
adamant
'stubborn' is the definition.
(thesaurus)
'a barrier worker' is the wordplay.
'barrier' becomes 'dam' (dam is a kind of barrier).
'worker' becomes 'ant' (worker is a type of ant).
'a'+'dam'+'ant'='ADAMANT'
'being' is the link.
(Other definitions for adamant that I've seen before include "Fabulous rock" , "Data man can be quite unyielding" , "Determined and unyielding to requests" , "Firm and unyielding" , "Refusing to be persuaded" .)