Recently, I saw a video clip of Donald Trump spouting off his usual meaningless "stuff that people want to hear" in which he said we "aren't a country unless we have a border". I am not sure what he is thinking. Most borders between adjoining countries are relatively invisible. There may be border crossing stations, but much of the borders are invisible to the naked eye.
The idea of building a wall has been tried before and, historically, has been overall unsuccessful. Examples include the Great Wall of China, Hadrian's Wall and the Maginot line. The problem with building walls is they eventually come to an end, and you can simply go around the end. If you are more motivated, you can also try to go over or under. The bottom line is that no country in the world has an impenetrable border, and probably never will. What is would take (money, manpower, and the willingness to inflict violence upon anyone trying to cross), is a price no one really wants to pay.
So, when the Donald says we aren't a country because we don't have a border, he is just making noise without substance.
There is more to being a country than having borders. Laws, culture, language, literature, education and industry are just a few examples. A less formal, but more realistic perspective on the topic (than Trump's) came from the late Frank Zappa:
"You can't be a real country unless you have a beer and an airline. It helps if you have some kind of football team, or some nuclear weapons, but at the very least you need a beer."
Even if you don't take him the least bit seriously, it's obvious that Frank Zappa put more thought into what he said than The Donald ever will.
Vote for Frank Zappa, and have a beer.
