If someone is outright trying to destroy your reputation how hard will it be to file a suit against a person for defamation of character

it is simple and easy to file suit, difficult to win.  In my experience, the two most common problems with defamation suits is that (a) what the defendant said or wrote is often considered a statement of opinion, not fact and (b) the plaintiff can't show any damages from the defamatory statements (although with some types of statements, it is not necessary to show actual monetary damages).