So, I thought I'd go to the Bunda Anarchy and interdict an Authority ship (they can't summon help in an Anarchy).
Nor can you...
[There are a few players based at Jameson Memorial who make very regular use of Bunda]
Oh, that's OK. I don't always fly in Open nowadays but when I do, I fly in a ship that nobody - not any number of bodies, nothing and nobody - not 12 of my best PvP frenemies in the same instance - can harm in any way, with any other build or combination of builds, if I don't want to be harmed, at all.
In fact, even interdicting one of my builds would be a sign of extremely challenged noob-ism. Whether I'm flying a small, a medium or a large.
Whilst I don't personally think 100% guaranteed invulnerability is good for the game, if anyone reading this thread is worried, I'd recommend flying something with 100% guaranteed invulnerability. It works!