Leaving aside the argument that tunnels go underground (thus rendering surface-obstructing fences moot), I would have to say that Bob Krumm's wish for a 6,500 mile fence is impractical and even dangerous to Americans on the border if you consider the complexities and legal implications (let alone the cost, which Republicans are generally unwilling to pay unless they can borrow the money) of actually building a border fence.
Quoting a report on one such plan for the Rio Grande Valley in Texas, the Texas Observer opines:
[T]he tactical infrastructure within several of the 21 sections [from Rio Grande City, TX to Brownsville, TX] would also encroach on multiple privately-owned land parcels. Some proposed fence sections could also encroach upon portions of the Lower Rio Grande Valley National Wildlife Refuge and Texas State Parks in the Valley.
....In addition to the possibility of legal entanglements from eminent domain proceedings, the Department of Homeland Security must also leap over environmental laws, and if it wants to use the levees, it probably needs Mexico’s assent as well. Then, of course, there is the widespread opposition from residents and elected officials from the Rio Grande Valley.