Okay, let me try to clarify my point more for you & for others in this thread.
First thing we need to understand is that in any country or situation (business, personal, etc), resources are limited, whether they are financial, human, time, etc. A top manager or leader needs to decide which expenditure of certain resources brings the highest benefit. The average person looks at his surrounding and wonders, "Why can't they fix this road, why can't they build a mosque, why can't they pay us higher, why can't they reduce tax, why can't they save the environment" and so on. But any expense means you are spending less on something else. The question is, which would be the best use of the resources?
Fortifying a 900+ km in mountainous terrain is extremely resource-heavy. Let's use the USA-Mexican barrier as an example. For almost the same amount of length, the project cost USA $2.4 billion! And while it brought down illegal immigration, it didn't make it zero. In 2010, there was still almost 463,000 illegals entering!
Now let's look at the problems we face with the border. Each countries border situation is different. We don't face a immigration problem (Berlin Wall made to prevent people going out, Mexican-USA border made to prevent people coming in). Pakistanis aren't illegally coming to Iran to find work nor are we having a problem of Iranians going to Pakistan to find work. Nor are we at war, like Koreans with their DMZ.
Our situation is two-folded,
1) Illegal Trade - Smuggling, Drugs, etc
2) Terrorist actions by Sunni Extremists from Pakistan
And I will propose that both situations have better solutions than pouring money into border control, which I personally believe never address the actual problem. Israel's wall doesn't address the actual problem of their situation with Gaza. Berlin Wall didn't address the shitty situation East Germany was in. And so on.
So, let's start with Illegal Trade
I knew Baluchis who would travel between the two countries. There are special drivers who know the mountainous terrain with their eyes closed. And I mean, literally with their eyes closed, because these guys drive at night, with their lights switched off. They do this so they won't be seen by patrols. Can you imagine how hard it is to even notice a car in 900 km border that is driving in the dark at high speed without any lights? This is why with USA's high budget, personnel (21,000 men and women!), and technology, they still have around half a million people entering per year.
Instead of spending millions on the border, use the money this way instead:
1) More campaigns in Iran to discourage people from using drugs
2) More camps for people who want to quit
3) Coordinate with Pakistani & Afghani government to see if it is possible to buy the raw drugs (such as opium) to use in legal medicines (such as codeine). Let farmers benefit more than the legal trade than the illegal one
4) Study if possible to legalize certain illegal drugs, and then discouraging traders to import it legally
5) Regarding smuggling of goods, look at better streamlining the customs procedures. Tariffs should be heavily reduced on goods between Pakistan & Iran to make smuggling pointless.
Now, let's talk about Sunni Extremists. Again, I find the money that could be used for border control can be used for the root of the problem.
Keep in mind our main objective should not be how to prevent Sunni extremists coming in to harm us, but how to reduce the tension in the first place!
The money can be used for:
1) Make the Iranian Sunni Borders an example of prosperity! Let the people from the other side of the borders see that a few kms away, their neighbors are living well under the Islamic Republic. Any of them from the Pakistani border who sits with his friend from Iranian border and talks about "Shia Iran", the Iranian Sunni will compare their two lives, and realize that he is much better off, and won't take his talks seriously.
2) Have lots of Sunni-Shia conferences and gatherings between the two countries. Let the two sides sit and talk and have events together. The best way to fight ignorance is through building relationships.
3) Spend money in Pakistan border cities. Build Iranian hospitals and clinics. Make wells for villages. Send free Iranian made farm machines. The extremist preacher who insults Iran at the friday mosque in a village, one day will be sick, and he will go to the Iranian hospital in the village, and this alone will make him look like a fool. And don't go to Pakistan to build Husseiniyas. The last thing a Sunni wants to see is Iranian government building a Hosseiniya in their city.
If we attack roots of the problems, we solve the problem. Walls have never solved any problem.