Hi Christine, you can "Marketing Suspend" people, which could be triggered to check/uncheck at specific intervals. When someone is Marketing Suspended, they won't be sent something through Marketo regardless of if they're on any send lists.
Another option, and my personal preference, would be to segment. If you can be diligent enough to ensure that your send lists contain a filter for the correct segment, then this is one of the most powerful tools that you can use to know where someone is in the buying stage, as well as who to target at any specific time.