During the development of your game, you should already do some marketing. This way you line up some customers to buy your game once its released. But marketing means revealing parts of your game. And when developing an innovative game, your primary fear might be that someone is going to steal your idea, and… (Tune from Jaws here) daaa dum daaa dum daaa dum… bring out a cloned game sooner than you! AAAARRRRGGGG!
Well… I got news for you: nobody is going to steal your idea.

Take a look at Braid or Tower of Goo for example. Both are innovative games, both revealed their concept long before their release. And you know what? Nobody stole their idea.
Next to these two masterpieces, I’m shamelessly going to use my own game Mystic Mine as an example. To be honest I was indeed scared that someone would steel the idea of those impossible “Escher”-levels. But you know what? Nobody did! And if you think of it, this makes perfect sense. Why would you clone a game that hasn’t yet proven itself in the market? And if it’s already popular before release, people are waiting for the original game, not the clone. Besides, are you sure you will put the game faster on the market? It just doesn’t makes sense to clone a game that hasn’t been released yet. And your fellow indie game developers, they all have their own game ideas to develop.

So market the hell out of your game while working on it, and don’t worry about someone steeling your idea or concept. Now go do it! What are you waiting for?