Right now Fences can not have fences within a Fence, but if I remember correctly there was a feature request put in for it sometime back. But, I would like to suggest to use Fences Desktop pages for that. For example. instead of One big Fence with multiple fences in it. You have one big desktop with all the game fences in it. And another desktop just for "Work", another for Media, audio video stuff. etc etc.
Stardock Community Assistant.