That's not a good way of getting around things in general. It's all mostly in your head, the possibility of someone actually stealing your stuff and then go on to make it big because of it are quite slim, almost non existent.
No one wants ideas, most people want results. Thieves don't want to put in the hard work. Ideas while great on paper, need the hard work to realize them, which is what gives them value.
If you are still worried, get feedback from people you trust, like friends and family. You might also consider people who are NOT into software development as they would be less likely to take interest in the nuts and bolts of what you are working on, and just look at the flashy colours on the screen.
On the same note, feedback from people who are only consumers of software, tends to be more honest because they are not aware of the struggle of game development. In short, they are more likely to say something that you might not want to hear, just because they have no idea how hard it is :P