I'm thinking immediate border land neighbors would be split, because the fence and it's attendant support would eat up some of their land, and change it's character. No more peaceful unobstructed view of the placid Rio Grande, por ejemplo.
I'd also bet that if you averaged responses over people within, mebbe 25 miles of the border, you'd find them overwhelmingly for it.
Well, of course we'll have to keep the river. There's no logic in giving it to Mexico. Think of it as a penalty against them for friggin' with us all this time.
We could even move the channel if we had to.