This is a such small change (of something that's bugged me for years) that I'm sneaking it onto the Xmas wish list:

"Your skin becomes covered in bark."
"Someone's skin becomes covered in bark."
"The bark on your skin flakes off."
"Your skin starts to toughen up but then turns normal again."

WTF? I'd imagine even in Thera rangers suddenly sprouting bark on their skin would be considered magical, so I propose you change the echo(es) to something else that doesn't imply mystical transformation. I haven't come up with an echo I'm really happy with, but I'd make it incorporate willpower/ignoring pain, something to the effect of:

"You harden yourself to shrug off cuts and wounds as if your skin were bark."
"Your skin feels normal / less like bark again." (wear off)
"You fail to toughen up your skin." (fail)

If you think the skill should (still) have a room echo, it could simply be:

"Someone concentrates intensely for a moment."

n/t

While fighting the watcher, I had bark skin and protection heat cold dispelled, and it specifically said "The magic of your bark skin was unraveled". If those specifically are non-magic, shouldn't that not happen?

n/t

I love the change to the barkskin echos but I think the barkskin fading echo is still a little off, bark is still "flaking" off.

I would like to suggest: your skin looses it's rigid bark-like toughness. Or your toughened barkskin returns to normal. Or your naturally toughened skin relaxes. Or as your concentration on your skin fades, it returns to normal.