My most effective curses have been jar spells with a link to the target inside. I guess it’s because I spent a few hours concentrating all the anger I had into them. I asked any spirit that could hear me to help. I’ve only banished and cleansed once so there’s probably plenty of dark energy around.
Maybe you could ask a spirit to give you an air of intimidation so people don’t even think about messing with you? When I lived in a major city, I made a habit of giving “the stink eye” to strangers. I often carry a weapon and send people the unspoken message “Don’t even think about it.” If you’re thinking about the most effective way to kill someone, people sense this and act accordingly.