Grails Shiro plugin : confirming my understanding

Question

I'm bit vague about how to start using the shiro plugin, after reading few documents. I decided against Nimble, as it comes with few tables and UI plugins.

I setup shiro plugin with wildcard realm, with my own tables. I may use permission based (rather tan role based) access control as it scales well. Now, the steps for it.

1. assign the permission string to the subject, and save it in the db
2. check the permission through isPermitted, hasPermission (or relevant tags in GSP).

Now,
1. when to use the accesscontrol through filter?
2. is there a closure injected into the controller where I can define the permission for the actions in it? I read somewhere about accessControl static closure on each controller, but not seems to be documented.
3. How do I create a typical access control scenario like only the creator of (something, a post etc) can delete it? One possibility is creating and persisting a permission string based on userid. to check the permission retrieve the object (post), get the userid and compare with subject.. seems bit complicated.. any easy implementation?

thanks a lot.. Babu.