Going quite a bit off topic here, but I'll bite:
Build a border that can be enforced
I hope you're not talking about building a wall. A wall is one of those ideas that seems pleasant, simple, and realistic at a quick glance, but when you get into details it starts to break down. Even the Great Wall of China failed many times.
Rather than trying to go back to Isolationist policies, we should be looking at A) why they come here, and B) what steps we can take to diminish A. In the long run, removing their need/desire to come to America illegally will have far more benefit for everyone than simply trying to hide the problem behind a chain-link fence.
A isn't easy; a lot of people will claim "because America is the greatest country in the world!" Except we aren't turning back a tide of Canadians at our northern border, so far as I'm aware, meaning either America and Canada are roughly equivalent in greatness or there are other reasons that Mexicans are risking quite a bit to come to the U.S. While I'm no expert on Hispanic relations, it seems to me that what is happening is not so much Mexicans wanting to come to the US, but Mexicans wanting to leave Mexico and the US being the most natural choice. (I'm not aware of Guatemala offering a lot, and in fact Mexico is facing its own illegal immigrant problem with Guatemalans)
The main cause that I'm aware of is the Mexican Cartels, who mainly use drugs as their source of revenue. The surging movement in America to legalize weed is having a growing impact on that. They still have crack and heroine, of course, but these are far more destructive drugs that will result in fewer return users.
There are likely other other factors, such as poverty, especially in the border towns (driving along the highway by the border in El Paso, TX gives you an eerie comparison between Juarez and El Paso, especially when you consider that much of the El Paso side is still lower class.) Government corruption might be a factor.
For B, I already mentioned the legalizing of weed in America. If we can change the discussion of our "War on Drugs" from punishment to rehabilitation, we could lower the demand for drugs from Mexico (and other countries dealing with the same thing) even further.
For poverty, I don't have a good plan. But let's consider that fence again. It could cost $22.4 Billion to build (though the full cost is hard to figure out, apparently). A quick search tells me that the estimated population amongst the six Mexican border states was 12,246,99... in 1990. So that number's a bit old, we'll bump it up to 20M (another source says 24M by 2020, but that's for both sides of the border.) With about 27.9% being kids, that's about 14M adults, giving us $1600/Mexican adult (more, actually, as the "kids" only includes up to age 14). The average yearly income for Mexico is about $13K, so that's significant but not huge.
What if, instead of spending that money on the border, we use it to improve the cities on the Mexican side of the border? They would give at least a small economical boost, though short-term, and while improving those cities we could have US law enforcement work with Mexican law enforcement to further route the gangs. This isn't without risk, of course, and a lot of people would like to see that 22.4 Billion invested in our own country through either education or infrastructure, but if we're talking about ways to fix the "problem" of illegal immigrants then I believe it will be far more useful to use money appropriated for such a task in that capacity.