Some sentinel on gate sleeps for stretches (9)
I believe the answer is:
elongates
'for stretches' is the definition.
('elongate' can be a synonym of 'stretch')
'some sentinel on gate sleeps' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'ELONGATES' can be found hidden inside 'sentinel on gate sleeps'.
(Other definitions for elongates that I've seen before include "stretches" , "Extends" , "lengthens the process" , "pulls out" , "tortures on the rack!" .)