Calling ideas "a dime a dozen" massively overestimates their value.

Form a team to implement it, or tell somebody who will, before someone else comes up with it independently. All else fails, shout your great idea in public (twitter works well for this purpose) -- otherwise, nobody will ever know that you thought of it.

Or, if you don't care about people attributing it to you, you can just keep it close to your chest. It's not like you're likely to make money on even a good idea anyhow -- the odds are against any new business making money, period.