✓OPINION ON THE PRESIDENT DONALD TRUMP'S BORDER WALL IDEA!

Well first you need to show that it's actually a problem. Since 2007 the % that illegal immigrants represent the population has fallen by 13% (and this is ALL illegal immigrants). In 2007 Mexican immigrants made up 57% of all illegal immigrants, and only 50% in 2016. In 2007 there were 6.9 million illegal Mexican immigrants living in the united states, while in 2016 there were 5.4 million. 
Sources:
www.pewresearch.org/fact-tank/2018/11/28/5-facts-about-illegal-immigration-in-the-u-s/
www.pewresearch.org/fact-tank/2018/12/03/what-we-know-about-illegal-immigration-from-mexico/

So knowing this, even if it WOULD work (which I'm not convinced it would just because of the shear size of the southern border) it doesn't even seem like we really NEED it, at least not according to the research (unless you think pew research is fake news, I guess, but if you think that you're beyond hope).