Another option would be to use
Event System on Page
Save and interrupt the saving if the Page Template <->
Component Template combination is not allowed. You can throw an exception with a meaningful message informing the Editors that what they're trying to achieve is not permitted.
The advantage of this approach is that you handle your specific case even before it's created VS throwing and exception from Templating or not rendering it at all (effectively masking the
Component Presentation). In other words, you have a clean slate as far as the PT/CT combinations goes, effectively having a clearer overview of the current state of the system.
Naturally, this also has drawbacks, for example it will get executed each time a
Page is saved slowing the system a bit, but the main concern is what about the already existing Pages which have the forbidden
Component Template. For those, you could use Core Service to do a quick search and remove the
Component Presentation from them.