Prepares for shock of Black Sabbath's touring marathon perhaps (6)
I believe the answer is:
braces
'prepares for shock' is the definition.
'black sabbath's touring marathon perhaps' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'sabbath' becomes 's'.
'touring' indicates putting letters inside (touring can mean going round).
'marathon perhaps' becomes 'race' (marathon is a kind of race).
'b'+'s'='bs'
'bs' placed around 'race' is 'BRACES'.
'of' is the link.
(Other definitions for braces that I've seen before include "Appliances to correct dental irregularities" , "Stabilises" , "Dental appliances and pairs" , "Couples" , "straps to hold your trousers up" .)