Hmm - I had a cheating boyfriends stuff packed into the bed of his truck and the locks changed by the time he got home from work once - many, many years ago. It worked well, and that was the last I saw of him.
That was a different time I suppose...
Yes, consulting the landlord and an attorney are great ideas, you never know how someone is going to react on D-Day.
Good luck - sending you positive vibes for a quick, peaceful ending - all that!