I installed it, on my system just to see how it works, and I removed it. This how I did it:
To completely remove Cairo dock, just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, run the command(s) below:
sudo apt-get purge cairo-dock cairo-dock-plug-ins && sudo apt-get autoremove
And to install:
sudo add-apt-repository ppa:cairo-dock-team/ppa
sudo apt-get update
sudo apt-get install cairo-dock cairo-dock-plug-ins
Also if you have Synaptic Package Manager installed, you can search for cairo-dock, and unckeck cairo-dock and cairo-dock-plug-ins.
You can go back to the USC, and remove Cairo Dock.
I just tried it on another machine, and tried the first command, install it form the USC it, and it was removed.
If it starts in maintenance mode, then do this:
Launch Cairo-Dock in a terminal with :
If you have the maintenance mode again, can you launch Cairo-Dock with
cairo-dock -ol debug
and post the output
One last thing. Install synaptic package manager if you don't have it installed. You can install it by just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, run the command(s) below:
sudo apt-get update && sudo apt-get upgrade
sudo apt-get install synaptic
Once installed launch it from dash, and when it opens search for Cairo
Highlight all Cairo entries
Right click, and choose Mark for Complete Removal