Giant shih-tzus regularly unmoved (2,4)
I believe the answer is:
in situ
'unmoved' is the definition.
(I know that unmoved can be written as in situ)
'giant shih-tzus regularly' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'giant'+'shih'+'tzus'='giantshihtzus'
The alternate letters of 'giantshihtzus' are 'IN-SITU'.
(Other definitions for in situ that I've seen before include "Already placed" , "American lift" , "At the appropriate location" , "Occupying the right position" , "Being in the original position, not having been moved" .)