First you need a flag field for this "locked by me," a number field. It would likely be on the layout as a checkbox, using a Value List of "1" (Boolean).
You need a Privilege Set for the "employees." In its Record access privileges screen, in the Edit access, add a test for "lock flag ≠ 1".
In the Fields access (same screen, on the right), set that field to be "read only" for them.
On the layout you could even hide the checkbox from them, by using the "visibility" trick.