Customs will stop them on aircraft or at border crossings.

Why would customs stop people from coming over LEGALLY on airplanes and at border crossings? Oh wait, they won't.

Also you pulled that 40% out of your ass. Source or bullshit. Here's a tidbit people like you and trump supporters ignore: A rising share of unauthorized immigrants have lived in the U.S. for at least a decade. About two-thirds (66%) of adults in 2014 had been in the U.S. at least that long, compared with 41% in 2005. A declining share of unauthorized immigrants have lived in the U.S. for less than five years – 14% of adults in 2014, compared with 31% in 2005. In 2014, unauthorized immigrant adults had lived in the U.S. for a median of 13.6 years, meaning that half had been in the country at least that long. Only 7% of Mexican unauthorized immigrants had been in the U.S. for less than five years in 2014, compared with 22% of those from all other countries (source: http://www.pewresearch.org/fact-tank/2016/11/03/5-facts-about-illegal-immigration-in-the-u-s/).