In order to stop someone from appearing on your visitors page, you must 'Ignore' that member. Visit the profile you wish to 'Ignore' and select the icon. Here you can select 'Ignore' and this profile will no longer be visible on your visitors page or in searches your perform.
The Visitors feature allows you to see who has viewed your profile while you have been away. You can choose to filter your visitors according to whether they are online or if their profiles have been verified.
To see recent visitors to your profile, select the icon underneath your profile image.