First 40% - 50% of undocumented immigrants enter the country legally and become undocumented by overstaying their visas. No wall, no matter the style or how high will stop visa overstays.
Second, a GAO report criticizes the Department of Homeland Security (DHS) for not having valid ways of assessing the effectiveness of border walls. Also, a DHS report points out that walls are ineffective barriers to people who want to breach them.