(more likely IMO given the attitudes of CSA leadership) leads to round two really early once Confederates decide they won't let the border impede their pursuit of "stolen property."
...because they just *have* to grab the idiot ball and do this without regard to odds of success or dangerous consequences. Because to be evil means to be cartoonishly stupid too.
Nah, I don't think so.
You know how the South works to counter the bleed off and escape of its human property? Hint: It's not militarized incursions and pursuit operations.
It is primarily about maintaining internal and border controls. For retrievals from across the border, Confederate property holders and authorities mainly use a softer approach, relying on a desire many northerners have that *competes* with the desire have to not send escapees back as a way to torque off the southern traitors; the just as genuine and widespread desire to not have nonwhite people loitering or passing through their communities, especially in large numbers.
Confederate property holders and authorities (and state governments), wherever they can, will make overtures across the border to municipal and county level Mayors, Sheriffs, business leaders and other officials and citizens groups of any of a white supremacist, Democratic, or Copperhead bent who can be persuaded or already believe it is in their community interest to not become a stop in the underground railroad or a refuge for runaway slaves or a host community for free people of color, and coordinate actions against escapees, abolitionists, and sympathetic ministers and journalists to efficiently and quietly detain and return escapees back over the border. Folks from the CSA side will likely help subsidize or defray the costs of their collaborators on the northern side, or outright bribe them.
On stretches of the Union/CSA border where there are no willingly cooperative collaborative local officials, politicians, citizen's groups, police departments present or dominant on the Union side of the border ready and willing to help return escapees, the Confederates who lose fugitives slaves that way just have to 'like it or lump it' and accept it as part of the cost of living and doing business.