Stop Planner completing a task when completed in an assigned persons To Do list?

Hi,

I have a Planner board where I've created individual buckets for meetings on various dates. Within that bucket there's different tasks with different checklist items which I want people to complete. Once they've done them I can check each task off as complete.

My problem is I have to assign the entire task to the people doing the individual checklist items, and as a result when it appears in their To DO list and they tick it off as done for themselves, it completes the entire task in Planner.

Does anyone know of a way round this?