I like the UDF approach because it is simple, does not tie you down to a
specific relationship between cells  and is simple to implement. You can just
place the formula in one cell  and replicate it down the column.



If you prefer, having a value in a cell rather than a formula, you can
easily do a cut and Past Special.



One of the benefits of the verification is that it can highlight problems.
It is far easier to check a couple of flagged cells rather than all cells.
You will also know that the likelihood of false positive would be low.