"How to" / "is it possible" to put a write lock to a table?

Hello guys!

We got a strange problem, some session that run some use case puts extra rows in a table.
This particular table should just contain a static numbers of rows.

We got problem to detect the session/use case that puts these extra rows in the table.

An idea that we got is to put a write-lock at the table.

When the session/use case is performed it hopefully will end up with some error in the logs.

Is there some way to put an lock to the table from for example Toad?

Best regards
Fredrik