Legal Question in Civil Litigation in California

Not unless you can prove he told it to a third party. A letter to you does not consitute libel or defamation.

It would not only have to be conveyed to a third party (intentionally, if it's just seen by accident it doesn't count), you also have to have suffered real damages from it.

Other than the points made by Mr. McCormick and Mr. Cohen, libel suits are not a good idea in small claims court, and a really bad idea in Superior Court. In Superior Court, you would be subject to a SLAPP motion, which stands for Strategic Litigation Against Public Participation. It is a special motion to strike your complaint that the defendant and his attorney could file at the outset, and it would force you to prove your entire case at the outset. You wouldn't be able to prove it, based on the facts that you have given, and when you lost the SLAPP motion, you would have to pay his attorney's fees. Just keep it simple, and go for the security and pet deposit, which the law treats as being a security deposit.