A proper wall and money.
Here’s my money idea:
You figure out which cartels control what portion of the border. Let’s say 3 cartels control the Mexican portion of the US/Mexico land border area and another 2 control the Mexican coastline.
I would get with each cartel leader and give them a large cash payment every year (for argument $50 million). Anyway, we count how many illegals come across in their zone and take away money for each one. The more illegals cross in their sector, the less money they get.
Combine that with a wall and the illegal problem is solved.
If we want to be bold, we tell the cartels that there’s a bounty on all illegals in the US. For each one they identify and get out of the USA (either deported, taken by them, or...by other means), they get a cash payment.
That would really solve the problem once and for all.
Sounds like paying tribute to the Barbary Pirates.
Interesting.