Access control to activity

Hello All,

In my current process I have a task being created and assigned to a specific user for approval when an Opportunity is saved.  But the owner of the Opportunity can delete/approve the task eventhough it is not assigned to them.  I am assuming I have something wrong in my access profile for the user that is creating the Opportunity.  Does this have to be a specific setting for each record type?  Or is there a global setting to state that a user can create an activity, change the status of an activity that has been assigned to them, but not edit an