The Pacific Coast mountain range starts only 12 miles east of the ocean. The border fence with Mexico has to go through about 60 miles of very rugged, remote mountains and deep valleys in Southern California. When I worked there in the Customs Patrol, there were places that had no fence or even border markers. We actually drove into Mexico one day on a jeep trail before the locals told us that we were about 100 yards inside Mexico.
About five years ago, an estimate of $43 billion was given for a border wall. If a wall was built of concrete like Trump first wanted, it would easily be $100 billion. The Mexicans taped him as he was whining to their president that they needed to pay for the wall because he had promised his voters the wall. There are Trump cult members such as my brother and the lady who is certain that Trump never lies. (The Washington Post has a list of over 4,200 easily disproved Trump lies).
A question: If you had $1,000 to pay for Obamacare for you and your family, would you give it to Trump as a down payment on his wall? Most people wouldn't give up that money. Another question: Would it be all right for Trump to shoot your close family member on Fifth Avenue? He has worked hard to sabotage and gut the Affordable Care Act/Obamacare and doesn't care that thousands of people would die each year. I know of people who would have died without that medical coverage.
The stench from the Trump cesspool is getting overpowering, but people will still crawl on broken glass for Don the Con. PS: The Great Wall of China had gates.