I regularly disobey guards close to second home (6)
I believe the answer is:
iodine
'i' is the definition.
('iodine' can be a synonym of 'i')
'regularly disobey guards close to second home' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'guards' is an insertion indicator.
'close to' suggests the final letters (the close/ending of).
'home' becomes 'in' ('he's home' can mean 'he's in'**).
The last letter of 'second' is 'd'.
The alternate letters of 'disobey' are 'ioe'.
'd'+'in'='din'
'ioe' placed around 'din' is 'IODINE'.
(Other definitions for iodine that I've seen before include "Disinfectant made from seaweed" , "Halogen element, atomic no 53" , "Element, atomic number 53" , "Solution applied to wounds as an antiseptic" , "Element used in medicine, photography and dyes" .)