Peter's very reliable (4)
I believe the answer is:
safe
I believe this clue is a double definition.
'peter's' is the first definition.
(slang term)
'reliable' is the second definition.
(I've seen this before)
'very' is the link.
(Other definitions for safe that I've seen before include "Free from risk" , "Metal container for valuables" , "Metal case for storing valuables" , "Harmless" , "Secure in metal box?" .)