Ricardo:

To expand on Vlad's idea.

Add a network username column to your lock table and create a watchdog process unlocks all records that are locked by users no longer attached to the network at regular intervals.

If your user can only log once in the system. Either release all locks when they log onto your system or immediately display the locked record(s) in Edit mode as soon as they successfully log in. If your framework is already data-driven, the second option may be fairly easy to implememt :)

Daniel