We are using the default Task list from a Team Site and would like to only allow those that the Task is "Assigned To" to edit the tasks. How do you go about enforcing this?
When we tried the "Advanced Settings", we found that "Only their own" meant only those tasks created by the current user.
It looks like you need to create an event handler that updates the permission on the Task everytime the assigned user is changed.
Quite a few people have had this problem in the past.
Check out this site for an example of the problems people have had. That said it should work out-of-the-box if you copy content when setting up the Task List.
Looks like, an event handler is the way to go. I found this page in some of my searching and it explains a lot of the problems related to this issue:
Email Notifications and Alerts - Sharepoint Tasks List
Unfortunately, the client wants no custom code and wanted SP Designer workflows and browser based customizations only...
How about Column View permission? It can make SharePoint Columns,list views or Item Attachments invisible or read-only to certain people. The flaw is that you need set it one by one.