Let me get this straight... You want to create a magic trick allegorical to the assassination of Julius Caesar... and a card trick is what you turn to?
Well, I guess it's the only way you'll get it into school. They're so paranoid about that nonsense these days...
My advice, simplicity and symbolism defeat viscera.
To that effect, select a card with a lot of white on it to represent Caesar. Do not actually tell anybody that the card represents Caesar. That's too corny and no one will take you seriously.
Create a gaffed duplicate by streaking the face with a red Sharpie. Scratch and slash up the face with an exacto knife. Make sure the cuts are deep enough to be visual, but not deep enough to penetrate to the other side.
Once everyone sees the normal card, switch it using your preferred method for the gaff card and do your favorite version of the Haunted Pack effect. Gaffed card is forced out and revealed to be slashed beyond all hope.
Do not, repeat, DO NOT tell people what represents what. You'll look like a schmuck. The deck in your hand is entirely incidental to the story you are telling. Do not look at it unless you have to.
That said, I still think the idea I just described sucks, but given that it's a school, they'd never let you get away with any of the better ideas I could come up with.
