Sheepdog tracks in pit (8)
I believe the answer is:
colliery
'pit' is the definition.
(I know that pit can be written as colliery)
'sheepdog tracks' is the wordplay.
'sheepdog' becomes 'collie' (collie is a kind of sheepdog).
'tracks' becomes 'RY' (abbreviation for railway).
'collie'+'ry'='COLLIERY'
'in' acts as a link.
(Other definitions for colliery that I've seen before include "Coal-mining establishment" , "Grimethorpe?" , "Where a coalminer goes to work" , "Pit" , "Coalmine and surrounding buildings" .)