Safeguard two companies working (6)
I believe the answer is:
cocoon
'safeguard' is the definition.
(both can mean to protect)
'two companies working' is the wordplay.
'two companies' can mean two substitutions for 'company'.
'company' becomes 'co' (abbreviation).
'company' becomes 'co' (abbreviation).
'working' becomes 'on' (on can mean working or activated).
'co'+'co'+'on'='COCOON'
(Other definitions for cocoon that I've seen before include "Pupa's protective case" , "protective clothing" , "secure environment" , "Larva case" , "Silken sheath" .)