[Magnum44]

The wrinkle in that plan is the Mexican side of the river is controlled by the cartels

Agreed, warning shots are not a good idea. Just set up a few hundred overwatch sights and establish fields of fire for each. Target the coyotes and smugglers.

[PIF]

Target the coyotes and smugglers.

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Who will then return fire with heavy weapons - you will lose badly.

[Hot Tabasco]

Target the coyotes and smugglers.

Can't do that, that's a declaration of war.........all that can be done is scaring off the swimmers and making them think twice about crossing the river.