The 10th man. The one to disagree regardless of the plan. The 10th man is the way to have a plan B ready to go. If 9 men agree to the plan, then it’s the 10th man task to say “no” and come up with an alternate plan.
Having this way of thinking will challenge the common opinion of the rest of the team, it will challenge the original plan. It would lead to invaluable discussion and the fleshing out of true opinions, possible problems, solutions, and provide a viable plan B as well.
Have a member of your team be the 10th man. Keep him/her always thinking about alternative ways to doing things. As you do this more and more, better plans will emerge and this method will become second nature to your team.