In my opinion a good way to avoid scope creep is to have a highly efficient planing stage prior to the submission of a final scope statement. Make the most out of each meeting and get all ideas on the table, try to think ahead about what is a feasible outcome for your product and really try to hone in on the aspects that are to be focused on and what is to be excluded. Once the scope statement is developed and well thought out, build a work breakdown structure and dictionary that sets boundaries for each persons duties. It might also be a good idea to have the scope written out on a white board in the meeting room for all future meetings so that it is always in the back of your team’s mind when they are navigating through future stages. As a project manager do not be afraid to site the scope statement as a reason for why a certain team member’s idea is being shot down, “Hey that’s a great idea John, but how can we keep that idea within the lines of our scope?” it is better that they understand that this is the reason why it can’t be done so they don’t get discouraged from contributing in the future.