Except, instead of dividing Berlin, it should stretch across the Greek and Bulgarian borders with Turkey. It needn't be the eyesore that that old monolith was. They could model it on the barbed wire fences Israel has surrounding its territory, which seem quite effective.
The more one reads of the Muslims pouring into Europe from Syria, the more it seems that Syria's neighbors -- Turkey, Saudi Arabia, Kuwait, Qatar, Iraq, Egypt, and Iran -- should take them in. (Why aren't they?) Even Afghanistan and Turkmenistan are geographically closer than Germany and France:
After all, those are Muslim countries, so having more Muslims in them should, in theory, prove less disruptive.
In the absence of a wall, all the European host countries -- like Austria and Germany -- should say that they'll willingly take in refugees only when Israel, Syria's next door neighbor, accepts them as well.
And, in the absence of a wall, all of these non-Muslim countries should make every immigrant renounce Sharia law, clitoridectomy, terrorism, and jihad before they are allowed in. They should also swear an oath of support for education for girls, and equal rights for homosexuals.
If they don't agree to these things, they should be turned back at the border.
Otherwise, the melting pot just becomes a time bomb.
This would probably just result in a lot of liars being let in, but it would at least give these countries a good excuse to deport any immigrants who showed any inclination to violate those oaths.
But, frankly, the best solution would be simply to not let them in in the first place.