There's a new DNS based filtering service from IBM, Packet Clearing House and Global Cyber Alliance been launched called Quad 9.

It's free to use and you can find out more here. The instructions of course are for windows and mac but the same DNS server settings can easily be applied in Linux.Their FAQ is fairly extensive and covers most topics. Cutting to the chase,

For IPv4 use

For IPv6 use 2620:fe::fe

There are no secondary servers so you may want to add another as backup from a different provider like Norton Connectsafe.