Avoid package to be update on Gentoo

It's possible with Gentoo to keep a version of a package and mark it as no updatable.
To do that, you have to modify (or create if it doesn't exist) the file /etc/portage/package.mask.
Then add the package version in this file.

Example :

vi /etc/portage/package.mask

>x11-drivers/nvidia-drivers-180.60

So when you will make emerge -p world, you will see :
[ebuild R ] x11-drivers/nvidia-drivers-180.60

So the package can't be update.