I agree with Construction At. Always document everything in writing.

Don’t make over-the-top accusations. Simply tell your landlord that you were very surprised that he came over without first notifying you, and that, in the future, you’d appreciate advance notice. Depending on the impression you want to make, you can write the letter yourself or have your attorney write it for you.

If you go to court, you’ll have a great advantage if you have documents to prove your point.