Okay, my previous post on this topic was fairly flippant. I guess the quickest way of dealing with a disagreeable idea is to mock it.
Now, a more reasoned approach.
Every choice in government has its costs and benefits. There are unlimited wants for the governments spending, but, despite some who think otherwise, limited resources. So you have to measure the Needs.
I just wanted to point out the enormous impact on the environment the fence would have, how feeble it would be to even a half arsed attempt to cross it because you can't defend the entire thing. So, look at it from a cost benefit analysis. How much would it really improve things? How much would it cost? What would be the secondary costs? All of those answers depend on what you perceive as necessary.
If you honestly believe that a non-fenced border is the real reason that you now have terrorists in your country. ( http://www.canada.com/ottawacitizen/story.html?id=aa4a4449-9f41-4e1c-8021-12f8c1c726a9&k=56437 ) Then to you there would be a much greater need to close that border up and a higher value in closesing it. Now if you look at the fact that several of the 9/11 terrorist were on the 'no not allow into the country' list and they smiled and walk into the states, (not even a fake passport) one might conclude that maybe just maybe that should be looked at before you build a fence in the middle of nowhere. (Much easier to make a convincing passport than to march 4 weeks in the middle of nowhere and hopefully not get eaten by a bear) And that is of course assuming that we let in every tom, dick and osama. How many of the terrorist for 9/11 sunk into the country?
Of course it is their country, and honestly if they really really wanted to they could build a 600 Yard deep fence with sensitive devices to detect tunneling and then man the entire thing. It would be extremely costly though, and use up resources that could likely be better used elsewhere to greater effect. Imagine a billion or two spent on rebuilding Haiti insted. :-D