Did dog, we hear, stretch? (5)
I believe the answer is:
tract
'stretch?' is the definition.
(a tract is a stretch of land)
'did dog we hear' is the wordplay.
'did dog' becomes 'tracked' ('track' can be a synonym of 'dog').
'we hear' indicates a 'sounds like' (homophone) clue.
'tracked' sounds like 'TRACT'.
(Other definitions for tract that I've seen before include "Pamphlet; area of land" , "Region; pamphlet" , "Extended area of land" , "Stretch of space or time" , "Religious treatise" .)