Issue Constitutionally authorized Letters of Marque to private citizens to patrol the border.
Letters of Marque for private citizens ... interesting idea.
A wall or big fence, combined with active patrolling, will indeed stop most of the incursions by human and drug smugglers. If your path is blocked by an obstacle, you can’t proceed forward. Simple enough.
I don’t believe a declaration of war is required for a state to post its own National Guard along the border. In fact, Article I Section 8 authorizes Congress to provide for calling forth the Militia (which the National Guard supposedly replaces) to “execute the Laws of the Union, suppress Insurrections and repel Invasions;” and our border problem looks like all three.
Paying for a National Guard presence might be sticky, but we can take those funds from all the welfare that we won’t be paying to border crashers.