Retiree using enclosures is charged every second year (9)
I believe the answer is:
pensioner
'retiree' is the definition.
(I've seen this before)
'enclosures is charged every second year' is the wordplay.
'enclosures' becomes 'pens' (pen is a kind of enclosure).
'is charged' becomes 'ion' (I've seen this in other clues).
'every second' indicates alternate letters (I've seen 'every second of' mean this).
The alternate letters of 'year' are 'er'.
'pens'+'ion'+'er'='PENSIONER'
'using' acts as a link.
(Other definitions for pensioner that I've seen before include "beneficiary of fund" , "retiree" , "One past retirement" , "Retired person" , "senior citizen" .)