Just continue calling the cops for noise disturbances, suspicious activity, etc. Over time it makes it inconvenient for them. If they really are selling drugs, it will impact their business and they will look for another ba<x>se of operations.
Buy a police Siren.
burn the house down
My shotgun helps keep them off my property.
I don't loan guns. You might consider calling the police every single day until they come out and take care of the issue. Enough police coming up and down your street will make them paranoid enough to go somewhere else for their illegal activity.
A banishing spell...?
You could try eally loud classical music at all hours...