Hiya - I've used sharpie myself, but you might want to check into the various communities online where you can get loads of tips:
- There's the unofficial Deck Runner Safehouse on Facebook
- There's the Wreck This Deck channels on the Black Armada Discord
- There's the unofficial Wreck This Deck discord server
- There's the unofficial Wreck This Deck Reddit community
- And of course there's the hashtag #WreckThisDeckRPG