For RMC
Create the item as a bonus item.
Either as
a +X to RRs vs informational spells.
or
a +X to RRs vs detect evil spells.
That will make the wearer rather difficult to perceive. . .the first variation would become obvious, as casters would keep getting a blind spot around the wearer, but the latter would be more subtle. . .since "Detect Evil" is a binary function spell, merely indicating evil when found, and not doing anything when it doesn't find anything, it's failing would not necissarily tip off the caster that the target is shielded. . .they just wouldn't detect as evil without a really successful casting and/or really poorly rolled RR.
Just a note though, you need to make the roll by 50+ to avoid detection. . .so you need to make the bonus rather beefy.
Now, the embedding general gives +5 per tier. . .but creating a +5 vs channeling item, or a +5 vs Informational spells item, is a lot more useful than +5 vs detect evil. . .this is akin to enchanting an item for skill, if it was "Gloves +5 climbing" vs "Gloves +5 for climbing ropes" is another example. . .I often allow as a house rule that making the bonus limited can multiply the scale of the bonus allowed. . .i.e. a General I spell might enchant "Gloves of Climbing +5" but also "Gloves of Rope Climbing +10" . . .by that same logic considering how "Detect Evil" is a tiny subset compared to "Channeling" or "Informational spells" I might allow that bonus to be multiplied x3 or x4 even. . .I'd need to consider that in context of the game. . .
But doing it that way, depending on how large a muliplier you choose to allow, you can get a nice beefy bonus vs "Detect Evil" out of a reasonably castable spell without having to make the thing an artifact.