Watch it happen again.
Unless we are willing to order the military to open fire and they will put women and children up front, they will get through, be processed and released into the US. Assuming we will not use the military to stop them, we need other means. Central American and Mexican countries and police are totally corrupt. If we spread enough money around, the local police will stop them and shoot them, if necessary. The cartel enforcers are also for hire. We could also infiltrate the columns and groups, and “persuade” leaders to turn around, sabotage vehicles, etc.