Keep it simple, just throw salt around it in a circle.
The wikipedia entry says they’re usually around the person to be protected, but I’ve seen plenty of fictional works and woo-woo demon summoning websites where the demon/spirit/energy/evil is bound in the circle while the summoner stands outside.
I, of all people, would be lacking if I didn’t suggest that all-purpose ancient symbol, used the world over as an apotropeic device, the Gorgoneion:
I put one on the cover of my book, and I can aver that it repels potential book purchasers like nothing else can. After that, Evil oughttta be a piece of cake.
What if you wanted something to enhance your own evilness? Like boost your dark side so you could become a Sith Lord? would you wear the pentacle or rune upside down?
Is “fascinus” pronounced “FASənəs” or “FASkənəs?” Now that I know that “fascinate” comes from a Latin word meaning “to perform witchcraft with a magical dildo,” I may want to bring that up in conversation.
A charm to drive away unwelcome guests? WANT! Can I get it on a doormat?