I used to ride my dirt bike out of El Paso into NM and ride along the border. It was a four-wire barbed-wire fence with a boundary marker every mile. Never saw a soul. There was a gate that was padlocked but little sign that it was used. But this was a long time ago.
If you look at this border on Google Earth, the further west you go the less there is. As the border leaves the rio Grande, in mexico there is vast nothingness.
To cross the border into the USA, there is no good place to start and no good place to go once the border is crossed.