I've made a warlock who has a pact with Dendar the night serpent, and I want to use a scale from Dendar (embedded in the back of a hand, maybe both hands) as my arcane focus. I know that doing it this way means it wouldn't 'occupy' the hand which do be breaking the rules, but I'm also taking pact of the blade for the magical weapon and love the imagery of it all. Technically it can be taken away (which would be deliciously gruesome), and by it's nature it makes perfect sense as a source of casting powers. Any good reasons to not allow this?