Dog again regularly tails suspect (8)
I believe the answer is:
alsatian
'dog' is the definition.
(alsatian is a kind of dog)
'again regularly tails suspect' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'suspect' indicates anagramming the letters (a suspicious or unusual spelling).
The alternate letters of 'again' are 'aan'.
'aan'+'tails'='aantails'
'aantails' anagrammed gives 'ALSATIAN'.
(Other definitions for alsatian that I've seen before include "Breed of dog" , "Large dog and person from northern France" , "Wolf-like dog" , "Large dog and someone from Alsace" , "Dog (from French border region?)" .)