Warhammer 40K Tactics VI: Chaos Bringing Eternal Darkness? I brought my flashlight.

[Cheesegear]

Oh, and one more thing:
Except the Librarian is an Independent Character himself, so that "be within 2" of a model in BtB" doesn't work for him. He can target only units he himself is in BtB with, regardless how close he is to however many other models that are in BtB with whatever. So, no, all you need to do to keep your Independent Character safe is to keep him out of BtB with the Librarian.

Here's how its done;
Have your unit in a circle surrounding the Independent Character of your choice.
When your unit gets Assaulted, the - let's say - Librarian should be an unengaged model in the centre of the circle. During your pile-in move, as the Librarian is unengaged, he can move 6" Pile-In wherever he wants. Including into BtB contact with ICs.

If the Space Marine player gets the assault on you, you are pretty assuredly screwed, but if you get the charge, it should be pretty easy to prevent the Librarian from being capable of attacking your Independent Character.

Only if the Space Marine player doesn't put his Librarian in the front of the unit (before Assault) to be Assaulted/Engaged first and unable to make a 6" Pile-in move wherever he wants.
This is - of course - not a tactic 'casuals' or 'new players' know. As a lot of people normally put their ICs front and centre of a unit. The worst place to be.

Like I said; Librarians are feared. 'Staying away from them' just isn't that easy against a tournament-level player.

I have seen a Space Wolf 'power list' with four Rune Priests doing just this. One of those Rune Priests was Njal Stormcaller. It wasn't pretty.

To be honest, it's only a problem for Orks (where most Warbosses carry Klaws and go last) and other I3 armies. If the Librarian can direct against you, you can direct against the Librarian. He's only got I4.
But, then you've got characters like Typhus, Skulltaker and Tyranid gribblies with Boneswords...And Swarmlord. Run. Run from the Swarmlord.