Locking the current row for edit when the value in a cell changes

I tried almost all the macros/Examples given in this forum . Sadly nothing works.

My Problem:

I have a sheet with values from A to L. If the value in the cell "L1" changes to "Approve" then the particular row alone should locked.
If the second row has the value for the cell "L2" is "Reject". Then no need to lock that row.

Any help will be much appreciated.