Symphony.

Is there a way I can implement some custom page access control logic in symphony? I'm using the members extension and it provides only role based page access control. I need to allow access to a page to only a specific member based on his "ownership" of the things that the page displays.

Not tested, but how about: create a section called Page access control, give it a Pages field and a Member role field, and then use a data source with the relevant filters to check that an entry exists which ties them together. On the frontend, if the current role and page combination aren't allowed you could respond with a 403 via your XSLT stylesheet using Page Headers.

I just reread the last sentence of your post:

based on his "ownership" of the things that the page displays

So I don't think what I suggested is quite what you're after. But I think it's a case of doing something similar, and, instead of using a Pages field, using (a) field(s) linked to whatever it is that you need to filter ownership of before filtering against these fields in the data source(s).