The Rio Grande is already there. He could fill it with alligators and call that his dramatic gesture, but there's something obviously foolish. And the Wall isn't going to be much more effective.
There are Border Agents in Texas who have offered some ideas that might work--drones, electronic surveillance, alarms that could direct agents to where crossings are in progress--but these suggestions lack the big razzle-dazzle of a WALL.
He made up a lot of shit during the campaign to discredit Obama. Not enough vetting for refugees. But there's 18-24 months intensive and very effective vetting by virtually every branch of National Security. Makes no never-mind, ain't enough. He's going to do extreme vetting. Maybe 3-4 years. Who knows? If he can throw our money at it run people around and make all the immigrants mad at him, maybe kill a few kids, a big splash...
Oh, year, and of course ObamaCare is horrible, horrible, horrible. Now he's got to come up with something better for his Insurance Companies friends, but some keep the parts of the ACA that his so-called constituents don't want to lose. He doesn't understand that it's a conceptual system he's trying to invent and not a conglomeration of parts. He's not used to that kind of "building."
Of course the Wall is the kind of building he IS good at, and he can really freak at that...but...how can he make the Wall prevent MORE immigration and allow for MORE departments than what has already been reduced during the Obama situation? He can't, of course, but he CAN make a gesture and slap his name on whatever he constructs. But again, the concept of slowing undocumented crossings is still pretty foggy to him.
This so-called "president" is really a pretty useless tool for whatever work this country has to get done.