Downgrading packages in Linux (and keeping them down!)

I kept hitting this same issue every time I updated packages in my Ubuntu at work. We have a certain build system that for some reason requires libtool version 2.2.6 rather than 2.4.2 that comes with Ubuntu. With the newer version, the build fails.

So I kept fixing this with

apt-cache showpkg libtool
sudo apt-get install libtool=2.2.6b-2ubuntu1

Finally I found a solution that should prevent Ubuntu from upgrading the version:

sudo echo "libtool hold" |sudo dpkg --set-selections

The same should work for any package.