How do you prevent double-booking of a staff resource?

When I layout a project with a number of independent tasks, and a fixed end date, I frequently get the same staff resource booked on several different tasks at the same time? How can i prevent this?

@finurliig If the double-booking of resources persists after leveling the resources in your project, OmniPlan should present a violation. If this isn’t the case in the project you’re working with, could you send it in so that we can take a look at why this is occurring? Our Support team can be reached at