Can you actually cross the fences without a visa? I mean it's just sand but one step you're in Mexico and other step in US. So how's this controlled? Or is it like a free zone (zoma libre)

Don't listen to the slob who answered you, even if you are from Mexico or the United States, it is impossible to cross the border, you can only cross border posts. For the wey who answered: they can't shoot you like that, why if it is to which side you cross illegally, they will only arrest you and deport you to the country you belong to.

First of all, There's no way you'll be able to enter Mexico with out getting shot or even arrested. And I'm pretty sure because I went there before, the border is heavily guarded. Don't mess with the Mexicans. Lol.