The answer is: Female bodyguards.
I've been on 5-6 AMLO meetings the past years and I've always noted now little security apparently surrounded him. For instance, one evening I was outside the PRD's national headquarters waiting for a ride and all of a sudden AMLO just walked up, alone. In my surprise I didn't get a chance to say or ask much beyond a a few pleasantries. No body guards in sights.
Here's a fascinating story from today's Milenio that addressed exactly the issue of AMLO's security. Turns out that Polimnia Romana Sierra, a personal assistant of sorts, has also been much in charge of protecting him wherever he has gone the past years (which are many places - he has toured every single municipality in Mexico at least twice now, unlike any other human being in Mexican history).
Polimnia offers quite a few interesting anecdotes. Did you know that he never sleeps in the hotel room assigned to him? Read more here.