Basically just sticking the gun in the front of your pants and pulling your shirt over it.
Mexican Carry has nothing to do with the front of your pants.
The method you are referring too is more Gang-Banger in nature.
Historically, Mexican carry originated following the Mexican revolution.
Civilians were disarmed, yet the Vaquero's needed a gun to do their job.
Wearing a gun belt was a dead giveaway when meeting a Federale patrol on the trail.
They took to no gun belt, and sticking a SAA with the loading gate open in their wide chaps belt behind the hip.
If they met a patrol, they could easily ditch the gun in a puckerbush along the trail, and retrieve it later after the army left.
There was no danger of it falling down their pants because they were setting in the drivers seat of a horse.
There was no danger of the gun going off, because it was a SAA with an empty chamber under the hammer.
Even if it did go off, all it would likely do is shoot another crease in your butt. Your femoral arterys are more in the front between your legs.
I might add that it works quite well with a 1911 too.
Glocks and other stuff with no safeties, not so much!
rc