Please, God. No wall.
An Israeli style border fence is more effective and less expensive.
Don't screw this up.
The secure fence act already calls for it and is being constructed all along the border as it is. Anyone driving on I8 in Southern California or Arizona or I10 in Texas has seen it. For example, Imperial California.
El Paso
I just drove half the border a few weeks ago on a cross country trip and the border fence and other security measures are well under construction. The areas where it isn't have geographical issues but still have other security measures.
The 'wall' talk was a 'ra ra' line. The funds are there, the construction is being performed all under the Secure Fence act. A 'wall' won't improve anything beyond what the currently under construction border security program is doing. At that, the secure fence act calls for different type of security measures optimized for the terrain it is protecting. Such as the images above. In the Imperial desert, it is a wall, in Juarez/El Paso, it is a secured fence similar to the Israeli example.