See Dimir Confidant.

This probably can't be printed as is, it's too non-interactive, but I wanted to look for mechanics that enabled a playstyle that felt azorius, i.e. defensive or controlling (without hopefully shutting the opponent out entirely even though that would be very appropriate to the flavour).

I'm not certain that reminder text doesn't cause some misinterpretations. I could someone reading that as a Ghostly Prison effect.

I'm assuming it means something like:

> Interdict (You can't be attacked. Opponents may pay for that player to ignore this effect UEOT.)

Alternatively it could be something like Web of Inertia.

The 'tech' of ignoring effects is only used in Leonin Arbiter and four other cards btw. I think it's more of a 'hack' in mtg rules along with 'treat something as though something' (ie. Phasing's "as though it didn't exist").

So back to the card's mechanic. As you point out, it's a mechanic that encourages players to not to do anything nor move the game forward closer to a conclusion, which is probably pretty bad. While I find it unlikely to create stalls on its own, it does at least seek to slow down the game considerably as players will be deciding between attacking and playing their cards.

Stonewalling is certainly a thing white does; and should get some support. But this kind of keyword which suggests multiple commons with it on.. that's gonna be too much of it. Huge boring "Na na can't hurt me" games.