The "quickest" fix is to simply ship them BACK TO the border, and put them on the other side of it.
Best done where the 30-foot wall is actually completed.
An "improved wall" in the future should have "voluntary exit ports". They should be designed like the exit gates in some NYC subway stations, with a steel "revolving door" that turns only one way and permits only an exit, not a return. Works great in practice.

The illegal should be told:
You have 2 choices:
- go to prison for a year, and then be deported
or- walk through this gate and you are "free".
... and let them take it from there.