Right now, start inspecting the F out of every vehicle entering from Mexico. Make them unload and then reload every load of cargo, and look in every container. If they don't get the hint in about 24 hours, just close the border. Mobilize whatever Border Patrol, ICE, military, and regular cops it takes to close it down, totally.
Put up a couple of tent cities.
Put them, and the entire world, on maximum notice that no flights in from MGH (Mexico Guatemala Honduras) will be allowed... everyone goes to jail if they try, especially the pilot.
El Salvador, Belize, et al need to pay attention also... they need us worse than we need them.
Close the border first. Then start complete inspections as a negotiated compromise. If the produce trucks back up and spoil, Mexico will want the wall and help pay for it.