How to insert Tamper-proof non-repudiation records in PostgreSQL

Hi,

I am developing an HIPAA compliant audit log application. This application
will receive audit logs from 5 different applications. I am expecting about
~4-5K/min of audit record insertions.

And as such one of the key requirements is tamper proof. Short of using a
gigantic hammer like http://bigchaindb.com/ how can I ensure tamper proof
and non-repudiation using PostgreSQL.?

How can I ensure the record once inserted cannot be deleted/updated i.e.
non-repudiation ?

Thanks,
Onkara