Establish an Immigration Processing Center in an inhospitable place like Attu, one of the Aleutian Islands. If Attu is too small, put it in northern Alaska.
Most of the illegals come from warm climates. Knowing they will spend months in the frigid north while being “processed” will be a disincentive to the more intelligent of the prospective border-crossers.
A bcc of my above suggestion was sent to the office of DJT.