trigger when database link is used?

We have a bunch of old databases (Oracle 10.2) that we need to migrate to Oracle 12.2.  Many of them have database links, many of which we suspect are no longer used.  As manpower is limited, the order in which the databases will be migrated depends on which links are still active.

Auditing is not enabled, and many of the databases cannot be bounced to for at least another few months to enable it.

Would creating a trigger to write a log entry somewhere when a db link is used be a fair way to investigate this?  The idea is to let these triggers monitor the links for a little over a month.