Live long, occupying time with dog (6)
I believe the answer is:
beagle
'dog' is the definition.
(beagle is a kind of dog)
'live long occupying time' is the wordplay.
'live' becomes 'be' ('be' can be a synonym of 'live').
'long' becomes 'l'.
'occupying' indicates putting letters inside.
'time' becomes 'age' (age is a kind of time).
'l' inserted inside 'age' is 'agle'.
'be'+'agle'='BEAGLE'
'with' acts as a link.
(Other definitions for beagle that I've seen before include "Type of hound" , "Short-haired dog" , "Hunting dog followed on foot" , "Breed of dog in a glebe" , "Small, sturdy breed of hound" .)