I decided to create a very simple group for the add-on tellmewhen that announces silences, stuns, pollymorphs and such to instance groups. It's essentially a way of telling the group that they're going to die.
The string below is active in all specs so if you want it only to announce in your healing spec you need to change the tellmewhen group setting.
For it to work you will need the addon tellmewhen and can import the string shown below. Visit the tellmewhen faq's if you need help importing the string.
Let me know if this is helpfull or just annoying :D