Enclosure is unpleasant without sodium (3)
I believe the answer is:
sty
'enclosure' is the definition.
(I know that sty is a type of pen)
'unpleasant without sodium' is the wordplay.
'unpleasant' becomes 'nasty' (nasty can mean unpleasant or horrible).
'without' suggests deleting specific letters.
'sodium' becomes 'NA' (Na is the chemical symbol for sodium).
'nasty' with 'na' taken out is 'STY'.
'is' is the link.
(Other definitions for sty that I've seen before include "Pig house" , "Piggery" , "Pigs' pen" , "Pig home or eye sore" , "Sore on eyelid" .)