Mark part of hog lying around bog, close to barn? (7)
I believe the answer is:
pfennig
'mark part' is the definition.
('pfennig' is part of 'mark')
'hog lying around bog close to barn?' is the wordplay.
'hog' becomes 'pig' (synonyms).
'lying around' is an insertion indicator.
'bog' becomes 'fen' (I've seen this in another clue).
'close to' suggests the final letters (the close of something is the end).
The final letter of 'barn' is 'n'.
'fen'+'n'='fenn'
'pig' going around 'fenn' is 'PFENNIG'.
'of' is the link.
(Other definitions for pfennig that I've seen before include "Former German coin" , "Former currency in Germany" , "Old German currency unit" , "Approximately two point two zero five pounds" , "Hundredth of an old Deutschmark" .)