Lettuce goes down for pets (7)
I believe the answer is:
cossets
'for pets' is the definition.
(to cosset is to pet or care for)
'lettuce goes down' is the wordplay.
'lettuce' becomes 'cos' (cos lettuce is a kind of lettuce).
'goes down' becomes 'sets' (setting is a kind of going down).
'cos'+'sets'='COSSETS'
(Other definitions for cossets that I've seen before include "Overprotects" , "Protects" , "Pampers" , "Treats with excessive indulgence" .)