Adding those pages to a Resource Group and connecting that Resource Group to the anonymous user group with a Resource Group Access ACL entry with a context of 'web' (or whatever the front-end context is) should work as long as the anonymous group has no users. Note that you'd have to visit the site from another browser where you're not logged in to either the Manager or the front end to test it.
If it really doesn't work, another alternative would be to use the Personalize snippet to show a different menu to logged-in and not-logged-in users. You could also create a plugin attached to OnHandleRequest that would forward users to another page if they were logged in. That would look something like this:
/* Do nothing if user is not logged in */
if (!$modx->user->hasSessionContext($modx->context->get('key'))) {
return '';
}
/* Forward logged-in users to another page */
$forwardPage = 12; /* ID of the page you want to send them to */
$url = $modx->makeUrl($forwardPage, "", "", "full");
$modx->sendRedirect($url);
return;
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