The saddest thing about Venice is that it suffers from episodes of high water, known as 'acqua alta'. Before we visited the first time, I didn't realize how serious this was, but I noticed the signs on this trip. Personally, from what I've read, I think Venice is doomed.
These high water episodes occur when the highest tides, typically in late fall, combine with winds out of the south coming up the Adriatic Sea. The wind-pushed water outside the lagoon prevents the normal tide from flowing out of the lagoon, trapping more water in where it can rise and flood the town. It's all in relation to historic measurements of 'normal tides', and starts getting serious when the water level exceeds normal by about a metre.
Given Italian politics, huge costs, and other problems, I just doubt they're ever going to be successful, though I hope I'm wrong.
Parts of this information come from the Wikipedia article on Acqua Alta, and you can find lots of Acqua Alta pictures here. You can read about MOSE here, and there's a great video of how Venice works which you can find here.