I always interpret scope creep as a way of the customer saying "I like what you are doing, do more."


The issue with projects with fixed timelines and fixed deliverables is that scope screep takes out any profit margin you hoped to get in the project. 


Do recurring billing, and use agile approaches like mentioned above. You really don't care if there is creep -- you just put it into the next "sprint" and charge accordingly for it.


Alex Sirota, PMP - NewPath Consulting - Schedule some time with Alex
"At the moment of commitment, the universe conspires to assist you." -Johann Wolfgang von Goethe