Double Jeopardy is a critical protection and its preservation is essential to protect people from frivolous prosecution. Not everyone can afford to be in court over and over again and unless there is a real strong proof that the person did it, there shouldn't an exception otherwise.
I agree that double jeopardy is important (and, though this is not really related, I think that a lawyer should be like an education- a good one is provided by the state, free of charge, with costs being recovered in the case of guilt) but I don't think that it should be absolute in the way that the constitution currently makes it. As I said before, I'm open to suggestions although I think most of the safeguards are better suited to legislation as opposed to the constitution.