I have several user groups on my website, like:

• Site Staff
• Departments
• -- History department
• -- Physics department
• -- Foreign languages department
• -- IT department etc

I also have several categories, like:

• News
• About
• ...
• Departments
  • -- History department
  • -- Physics department
  • -- Foreign languages department
  • -- IT department etc

Users in Site Staff group can edit entire site, except for Departments categories (I've set Deny permission for it). Each Department user group can edit only its corresponding category.

I have successfully implemented all this.

The question is: If a user belongs to two groups (Site Staff and Physics department - for instance) - he should be able to edit the whole site, except for Departments category. And also he should be able to edit Physics department category - this is what I cannot implement.

Can you suggest any ideas?