Yea,, Sure we don't..
We need to build it high and anchor it deep... And load up the whole length of it with sensors to catch em digging their tunnels.
Check out
this article. I especially like the comment calling the occupants "suspected illegals"!! We suspect that the 28 people with black hair and dark skin in this van that was running from the Border Patrol are actually illegal aliens.. Nawww,, they were just coming home from a Boy and Girl Scout Jamboree in San Ysidro!!!!

Yea,, I know the comment is true, they really are suspected illegals,, but let us for just a moment figure the odds that anyone other than possibly the driver is a citizen of the US,, or even in this country legally!! Not very da** likely..