Guard club, securing implement (11)
I believe the answer is:
screwdriver
'securing implement' is the definition.
(implement used to secure things)
'guard club' is the wordplay.
'guard' becomes 'screw' (I've seen this before).
'club' becomes 'driver' (driver is a kind of club).
'screw'+'driver'='SCREWDRIVER'
(Other definitions for screwdriver that I've seen before include "Common tool" , "Hand tool - cocktail" , "may make a fixer tight?" , "that'll turn a few heads" , "Woodworker's tool" .)