[Ruy Dias de Bivar]

A simple chain link fence with a V top and barb wire should do the trick! I remember adds for such fences back in the 1950s showing Edmund Hillary trying to get over one using mountain climbing gear, and he could not do it.

But then, that was the 1950s.

[Col Frank Slade]

I read that Border Patrol prefers a steel barrier wall because they can see what is happening on other side.