Yes, you can secure the access to the page through the page permissions set (for the CMS users) as you did, but you also need to deny anonymous access. This will ensure that unauthenticated public users are not able to view the page even if they know the URL to the page. Here is how to do it:
1. Select the page in the site map.
2. Go to the Properties
3. Expand section "More Options".
4. Select the Deny
option for Anonymous Access
Doing this will remove the page from navigation for users that don't have permissions to view it. Authenticated users that don't have permissions
to view the page will not be able to visit the page using it's URL directly.
the Telerik team