North Faron Woods - Howling Stone Location & Song Combination
The Howling Stones in north Faron Woods can't be reached until the game sends you over to the Sacred Grove as a Wolf (before you can change back and forth between Wolf and Human). If you miss the Howling Stone at this time you'll need to wait until much later in the game when you return to the Sacred Grove to tackle the Temple of Time.
The Howling Stone in Faron Woods can be reached by Warping to Northern Faron Woods and traveling north as if you were going to the Forest Temple. Instead, however, you use Midna and jump along the roots/ledges towards the Sacred Grove,
If you haven't gotten the Master Sword yet or if you aren't on the quest to get it now you will not be able to get over to this location.
Once you finally make it to this Howling Stone you'll need to Howl a very familiar tune to unlock the stone's power. The song, if you don't recognize it, is Zelda's Lullaby. For anyone who struggles with Howling the tune correctly take a look at my screenshot for the proper combination of notes.
After successfully Howling the song you'll get a brief cutscene followed by a location marked on your map that's just south of Castle Town. Visiting this Golden Wolf and speaking to him will unlock the secret skill Shield Attack.