What does the euro zone lack to prevent public debt crises?

The recent crisis in Italy shows that public debt crises can still occur in the euro zone and that , further , there is contagion: the rise in Italian interest rates spread to Spain and Portugal. How can the recurrence of debt crises, which weaken the euro-zone economy , be prev ented ? In the case of a liquidity crisis and not a solvency crisis , there needs to be a mechanism to correct liquidity crises and prevent contagion to the other countries ( a euro-zone IMF) . Solvency crises must be averted or at least stemmed either through stricter fiscal rules to prevent such crises or through a mechanism to resolve them if they cannot be averted.