The Collaborative International Dictionary of English v.0.48:

Stalking-horse \Stalk"ing-horse`\ (st[add]k"[i^]ng-h[^o]rs`), n.
   1. A horse, or a figure resembling a horse, behind which a
      hunter conceals himself from the game he is aiming to
      kill.
      [1913 Webster]

   2. Fig.: Something used to cover up a secret project; a mask;
      a pretense.
      [1913 Webster]

            Hypocrisy is the devil's stalking-horse under an
            affectation of simplicity and religion.
                                                  --L'Estrange.
      [1913 Webster]

            How much more abominable is it to make of him
            [Christ] and religion a stalking-horse, to get and
            enjoy the world!                      --Bunyan.
      [1913 Webster]

WordNet (r) 3.0 (2006):

stalking-horse
    n 1: a candidate put forward to divide the Opposition or to mask
         the true candidate
    2: something serving to conceal plans; a fictitious reason that
       is concocted in order to conceal the real reason [syn:
       pretext, stalking-horse]
    3: screen consisting of a figure of a horse behind which a
       hunter hides while stalking game
    4: a horse behind which a hunter hides while stalking game