You can set up a password to prevent people from moving between Self-Registration and Admin Mode.
In Admin Mode, navigate to Options > System Setup > Self Registration
In the Layout section there is a field called Password
Enter your password into the blank field. It is automatically saved.
To move to Admin Mode from Self Registration Mode enter the password into the name field.
Leave the cursor in the name field and click/tap the VisitorRego.com text in the top left (or bottom right of older software versions)