All,
  Secret of the Unwalked Path for urban setting In other words it counters Secret of Shadowing.
  Is this broken? Has anyone tried it? Any caveats?

For those following at home: Unwalked Path is a little Secret that allows a character to use his Woodcraft to resist attempts at tracking him in the wilderness.

The only way this'd be broken would be in that it implies an inability for characters without this Secret to do this sort of thing. That might or might not be appropriate for your game. I'd probably not use this sort of thing for most urban settings, as being able to lose shadowers flows naturally from any sort of local knowledge skills, with no special feat required.

Eero,
  I see it as a clone of Unwalked path meaning:
1) Any character can Shadow this character using the appropriate ability (Streetwise maybe?).
2) If the player spends the pool, then they make a roll which resists any attempt to shadow them (this is an Effect, right?).
  Does that make sense, is that broken?

… depends.

The existence of a given Secret is not inherently a sign for brokenness, since every character in the game world can try to learn and get it. If one you make up on the spot is too intrusive (i.e., anybody wants it since it's so effective), you can either change it into something that is a bonus die source instead of an effect enabler, or you introduce other similarily effective Secrets for other tactical choices.

See, if you put in a Secret of Counter-Shadowing, you actually change your Setting in a way that only people with that Secret have a way to counter the effects of Secret of Shadowing. Without it, you might be able to create an Effect to counter Shadowing by way of various abilities (Perform(I) for Rockerboys who rig up a live performance to vanish after they summoned a number of crazed fans, Funds(R) for Corporate Drones who just buy a couple of street bums to distract you,  Street Medics who steal on their DocWagon Platinum contract, Gangers who use their Gang to throw you off their trail, etc.); with it, any of these tactics may not be efficient unless you have the Secret.