I am outside but inside. I have no roof but I am part of the house. What am I?

Deep in dank dark places, I grow down, testing humanity's patience. Water and time ensure I grow and grow, while ages make me grand. I hang about but never fly, the tortoise of fabled fame has nothing on me.

Did you hear they arrested the energizer bunny? He was apparently charged with…

I am a simple wooden tool that helps a vessel glide, A lever cleaving water to defy the pulling tide. Now drop me right between two letters, and I will quickly turn, Into a flat and wooden plank, a thing to ride or burn. Add a letter to my front, and brutal strength you'll meet, A fierce and charging forest beast with hooves upon its feet. Prefix another letter, and my weight begins to clear, I lift away from earth to float and softly disappear.

The house wears me like a cozy hat, while I keep it safe from this and that.