emerge -av --depclean wants to remove
sys-kernel/gentoo-sources-2.6.30-r7 after a world update.

How do I prevent this? I've tried the --deselect and --noreplace switches but that has the opposite effect I'm looking for.

I read this same question earlier this year on the gentoo-user mailing list and got a perfect solution from Mike Kazantsev along with help from Boris Fersing.

Edit (or create) /etc/portage/sets.conf and put this inside:

[kernels]
class = portage.sets.dbapi.OwnerSet
world-candidate = False
files = /usr/src

Then edit/create /var/lib/portage/world_sets and add this line:

@kernels


Now --depclean should never try to remove your kernel packages! It
works great for me.