How do I remove an unwanted house guest permanently?

Assuming your guest goes out once in a while, change the locks in his or her absence. How do I remove an unwanted house guest permanently?
Make them think you have mental problems. Like talk to yourself and mumble around. haha I think that would warn them. Oh yeah walk around in your underwear. They might never want to come back.How do I remove an unwanted house guest permanently?
Tell them to leave and not come back, and tell them why.