3 words: supply and demand.
The so-called "War On Drugs" is just as successfull as the prohibition of alcohol in the US was. With the same side effects: criminalizing citizens for victimless crimes and a rise of the mob.
So all efforts in history failed so far to reduce the demand for drugs, what can we do with the supply? Imo legalization/decriminalization is the only effective way. If people do no harm to others only to themself I see no reason to punish them for this.
The US can easily provide itself with drugs, no need for imports. This way you'd dry out the Cartel's profits. Yes, they do not only make money from drugs, but the argument that they would switch to other criminal activities is moot, as they do it already.
Regarding illegal immigration it should be the other way: With billions of people worldwide living in poverty the supply is virtually endless. So here it could work to hit on the demand. Punish the employers of illegals. The demand for illegals is more or less a luxury demand, it derives from greed and cheapness, as most illegals provide non life-essential services. Can't build a sundeck because US workers are too expensive? Tough crap, maybe wait a year and save some pennies to afford it!
If there are not enough qualified people there is still the option to give out work visas. This way the foreign workers also have the advantage of being protected by work and wage laws.
About the efficiency of the wall, here are some official numbers by the Stasi regarding the German border, for the years 76-85:
http://www.chronik-der-mauer.de/inde.../file/id/44085 The first column is relevant, these are the successfull attempts (gelungene Fluichtversuche). 600-900 people per year seems pretty effective.
But does the US really want its Southern border to look like this?
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