I have an idea for a post you may read it and give your thoughts about actually posting it to the meta.
Here in this post put challenge ideas that you are not planning on using (or just don't want) and others in the community can comment and say they are going to use it.
Post your challenge idea and a few details and leave it. Community Wiki it so users can edit it and say they are going to use it in a post. People who take do not need to ask and do not post it here if you are not willing have the idea used without additional permission. If at one point you want your idea you can just remove your post.