Brad's secure (4)
I believe the answer is:
nail
I believe this clue is a double definition.
'brad's' is the first definition.
(brad is a nail with rectangular cross-section)
'secure' is the second definition.
(both can mean to apprehend or capture)
(Other definitions for nail that I've seen before include "Hit this on the head to be absolutely right" , "Finger feature (and tooth?)" , "Hammered individual" , "Perfectly execute" , "Small metal spike" .)