I feel strongly that President Trump's dogged determination to get money for his "Wall," rather than simply increased border security measures, is his vainglorious ego.
The Wall is to Trump what the pyramids were to Pharaoh Ramesses II, who, according to the poem by Shelley, is to have said "My name is Ozymandias, King of Kings; Look on my works, ye Mighty and despair!"
He wants a monument to himself, in the form of a large imposing structure he can stand in front of to cut a ribbon, for the ultimate photo op. The message of that would be "Look at how wonderful I am! I told you I was going to build a wall, and I did!" He might even say in in those exact words.
All the important parts of increasing border security, like increased use of electronic surveillance, higher number of Border Patrol officers, improved patrol vehicles, impenetrable fencing along the whole border, wherever possible, motion detectors, alarm systems, a road that runs along the whole border for easier patrolling, camera-equipped drones in constant patrol, or anything else that can be created by border security staff who know what is needed, would not have the same visual impact made by that one single photo nor give him anything to point to and say, "See what I did!"
I understand there is already funding for a piece of a wall being built along part of a dangerous crossing point in Texas, that will be started perhaps in February. Maybe he can be mollified with a face saving photo op there, and let any future funding go where it will do the most good.
Distracting someone away from something they shouldn't have, by offering them something they might like as well, is a technique all parents know. Maybe that could work here. We can only hope.