Access to submission row based on data content

We are working on a multi practice healthcare webform system. Patients will be asked to fill in a questionnaire about their health status during treatment on a regular basis. Forena will be used to graphically report status improvements.
Access to patient submissions_data is only allowed for practitioners from the same practice (that is involved in the treatment).
We have implemented the webform module in a way that patient can enter questionnaires and practitioners can view all webform results. This works great, only practitioners have now access to all patient data, not only from 'their own' practice.
As both patients and practitioners have a field 'practice' in their user fields, we would like to filter the results presented by the Webform module based on the practice fields of the current user and the practice field of the user who made the submission.
Nb. the practice field are protected against changes by the user with a rule in the Rules module.

As a first step we have used the Views_php module to enter a php filter in the view submissions as used by the Webform module.

But we still have a "leak" now as in theory practitioners can find patient results by "hacking" the url or, worse even, use the download to download all patient responses.

Would anyone know a better way to implement this submission_data access control requirement?

Any help would be great !

Thanks