My take on your power...
The power is an excellent idea. Drawing from examples in other sourcebooks of similar abilities, here's how I might put it:
Defender of the Realm (Ex): The king's warden develops exceptional tactics in defending his realm from the depredations of creatures that are common threats therein. The warden may select a number of opponents equal to the power level of this ability (subject to GM approval). These foes must come from a narrower selection than the ranger's favored enemies; the warden may not select "orcs", but instead must select some specific group of orcs like "the Green Tooth Orcs of the Blarkney Hills". Further, the warden may select members of his own race that come from a group opposed to the warden's protected dominion—soldiers of an enemy empire, for example. Even a diverse group that creates a common threat may be selected, such as all bandits from a local region. The warden's familiarity with these creatures, groups, or peoples grants him a +2 dodge bonus to AC, a +2 bonus to attack and damage rolls, and a +2 bonus to Sense Motive checks. These bonuses stack with favored enemy bonuses from other class abilities or feats.
One might also consider giving the warden a bonus attack of opportunity should such foes be caught in a condition that allows such an attack.
What do you think?
(EDIT) BTW, I want all authors to come up with an iconic character example for their class. If this is too much for anyone, let me know, and I'll make the character using your class. Add new magic items and spells for your character if you want (subject to editing, of course). Feel free to expand on your class with additional information. For example, the king's warden begs for an accompanying prestige class: the deputy warden.
On that note, this is why the Legendary Class should also have an iconic name. A deputy warden could just as easily be called a king's warden. If the leader of such wardens were called, say, Royal High Warden, the distinction would be clear. There's only one Royal High Warden, but there could be many king's wardens.
This is why I'm changing my class' name to something more singular—from Green Warden to High Guardian of the Green, Land's Heart Guardian, or some such thing (still tossing ideas about). Perhaps I'll make a prestige class to signify non-legendary members of the same order and call them green guardians (to distinguish them from the king's wardens).
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