Well effectively if attacking you will cost more than not attacking you, the foe will go with not attacking you. In crowded quarters, moving to melee with someone who is trying to stay at range can be nigh impossible.
Night, but not actually impossible. We might not be at cross purposes here; my point was that the right way to deal with the "I'm at range, you can't hit me" aspect of a ranged defender is that the "I'm at range" bit should be factored into their defenses (at least against melee) -- rather than forcing them to have a melee proxy which can take hits for them.
opponent. It's not going to break the game any more than if a ranged striker did the same.
To be fair, it wouldn't be a single encounter--at high paragon, it could be every encounter (just multiclass to Avenger and learn to fly; before that, get a flying mount). But there's already a defender who can mark at range (weaponmaster fighter) and one who can punish at range (swordmage). And the paladin can do both, but not effectively unless you build an Implement or Hybrid paladin (there's your existing ranged defender: the paladin/warlock). Being able to do both is a big bump, but still not that bad, particularly if you don't have full Defender AC/HP.
Which is why I mentioned until level 9.
From level's 1 to 4, the abjurer is a defender for one fight.
...
Unless the wards work like the summoned creature for the necromancer/nethermancer (in which case they all need to be moveable) you still have the general "all effects end after 5 minutes" rule which means you'd need to create a new ward in each encounter.
I explicitly referred to "all day dailies", so yes, I was referncing the necromancer/nethermancer; sorry that wasn't clear to you.
My thought there would be that the daily would read something like:
Abjurer's Warding
Standard Action
You gain an abjurer's warding, which has 10 hit points, plus your con bonus, plus plus 5 hit points per level. While you have this warding, gain +3 AC while you are wearing cloth or leather armor, +1 to all defenses, and resist(3) all. [ 11+: resist (5) all, +4 AC; 21+: resist (7) all, +5 AC]. This resistance stacks with other resistances, but whenever you take damage, reduce the warding by the damage it resists.
Special: This effect ends if it runs out of hit points or when you take a long rest, but not at the end of the encounter.
Special: Whenever you spend a surge, the warding regains a quarter of its hit points.
And then have powers that are worded "if you have a warding...".
Of course, my hp numbers are off; it's hard to make a balanced effect that would give a wizard equivalent hp to, say, a paladin (although forcing the wizard to burn multiple dailies at higher levels to keep up at least helps the balance a bit). A first level paladin functionally has 99 hp (assuming a 12 con), whereas a first level wizard has 75 [assuming a 14 con, as we're talking a con secondary class]. The same 11th level paladin functionally has 408 hp, whereas an 11th level wiz (now with 18 con) has 252 hp, so things are hard to keep balanced.
