Metal item used to control pet (4)
I believe the answer is:
lead
I believe this is a double definition.
'metal' is the first definition.
(lead is a kind of metal)
'item used to control pet' is the second definition.
(Other definitions for lead that I've seen before include "Go ahead; element" , "Top actor" , "Be in charge of, element" , "1 down, symbol Pb" , "Advantage" .)