Some people, given a choice between "building a fence" and "securing the border" will choose "build the fence".
Even where it's a bad idea.
Like along a river passing through an arid to semi-arid area.
For guidance, perhaps we should check out how the Israelis secure the River Jordan border between Jordan and the West Bank.
It's not a fence. It's a series of armed outposts, connected by a road.
Blocking access to a river coursing through a semi-arid landscape will inconvenience only your own citizens. While enabling the citizens of the country on the opposite bank.
Perry proposes the same plan.
You cant waste time out in the Negev desert.