I'm working on a super hero webcomic, and I need a motto for a SHIELD knockoff called AEGIS (Advance Enforcement, General Intervention Service). I've searched the Web for Latin translation pages and I have a vague idea of what I want. The phrase is "Defend Freedom", and the Latin seems to be either "libertas tuebor", "libertas tueri" or "libertas tuero". Thanks in advance for any advice!
Edit: Thanks to everyone who replied.