To be pedantic, defamation of character via Facebook is libel not slander. (Libel applies to a defamatory statement which is 'published', as on a web site).
Neither slander nor libel requires you to mention any names. If the person is identifiable (because, for instance, you've said that they live next door to you) it's still possible for an action for slander or libel to be taken against you.
However, slander and libel are civil matters, not criminal offences. You can't be arrested and the only way that someone could take the matter to court would be to fork out thousands of pounds (or, more likely, tens of thousands of pounds) to do so themselves; there's no legal aid available for such cases.
Your neighbour might try to claim that your actions amount to harassment, which is a criminal offence, but it's unlikely that you'd be arrested for it because:
(a) your Facebook jottings weren't meant to be read by your neighbour;
(b) "in the particular circumstances the pursuit of the course of conduct was reasonable" (that's a legal defence) ; and
(c) you're moving away anyway, so there's no need for the police to act to prevent future tensions between you and your neighbour.
Chris