Head of force in demand over church security (7)

'security' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

'head of force in demand over church' is the wordplay.
'head of' says to take the initial letters.
'in' indicates putting letters inside.
'demand' becomes 'need' (synonyms).
'over' is a reversal indicator.
'church' becomes 'ce' (abbreviation for Church of England).
The first letter of 'force' is 'f'.
'f' placed within 'need' is 'nefed'.
'nefed' reversed gives 'defen'.
'defen'+'ce'='DEFENCE'

Can you help me to learn more?