Here's an idea. Almost certainly not a good one, but an idea all the same and none of the alternatives seem particularly good either so it is worth thinking about...
The Euro, as it is, is currently a disaster that has already happened to Greece and will slowly happen to Spain, Italy, Portugal and others. Culminating in Germany, who won't get any money back when everyone else goes bust.
It is clear that the value is much too high for some countries and much too low for others, and that internal devaluation is extremely painful and difficult when there is no inflation. And it is also clear that individual central banks need control over interest rates. If there is to be no fiscal union, then there can not be this level of monetary union. Anyone but a madman (or possibly someone running a giant trade surplus thanks to an undervalued exchange rate) can see that there is a big problem here. But working out what to do about it now is another matter.
So here is a suggestion...
My idea:
1) Suddenly announce that all euros are temporarily to become national euros. All depositors and borrowers in Holland as of tomorrow will own/owe Dutch Euros etc. All Dutch government and corporate bonds are redenominated into Dutch Euros. Anything that can be tied to a nation is to be redenominated.
2) Then allow the separate currencies to float against each other. So one German Euro may trade at a rate of, for example, 1.2 French Euros. The adjustment would take a while to stabilise, so maybe leave it 3 months. In this period all banknotes will be stamped with the country they are from and can only be used there or exchanged at a bureaux de change.
3) After stabilisation, change everything back into old Euros but at the new market rate. This would be set broadly at the average traded rate, but by an independent committee to discourage market manipulation of the rate.
4) Repeat this whenever great imbalances build up in the future. Maybe only for affected countries in the case of a local crisis.
5) Give individual central banks power to set interest rates in their domestic markets in future. So Euros in Italy could earn more interest than Euros in Belgium.
The Euro will become a fixed exchange rate regime with periodic adjustments of the rate where necessary. Everyone will be aware of this and so know the risks that they are running. However, the ease of cross border trade remains from the current system. So it would become a sort of currency peg with benefits.
Not realistic, I know...
I know that this, even if it were the best idea in the world, is impossible. For one thing it would need to be secret, and something as big as this can not be kept secret. For another, no-one is going to do anything about the crisis coming up until it is too late because the the politicians have convinced themselves that there isn't going to be a crisis. And even if they believed there was, they still wouldn't do anything.
But it is an interesting thought experiment all the same.