XenForo has a built in "Discourage User" Option which makes it difficult or impossible for a user to navigate the site. It's similar to the very popular vBulletin mod called "Miserable Users". Basically, navigation slows way down, error messages randomly pop up, and sometimes you end up on pages you don't expect to see. This slows down unwanted visitors and sooner or later they leave, especially if they think the problems are sitewide rather than aimed at them individually.
I invite all affected members to our website where we treat all users equally and fairly."