Excel: Protect formula without using data protection

There's a nifty trick in Excel that allows you to protect formulas without turning on sheet protection. Why is this a good idea? Protecting sheets causes a lot of other problems such as blocking the addition of addition columns and rows etc.

The trick is to apply Data Validation after entering the formula.

Here's a short instruction on how to do it:

https://www.exceltip.com/excel-security-protection/protecting-cells-containing-formulas-in-an-unprotected-sheet.html

Another variation is to set the Text Length to an arbitrarily large length:

To ignore the inevitable green "Data Invalid" triangles once the data validation is applied, just select all the cells (starting with the first "invalid" cell), scroll back to the very first cell, click on the yellow exclamation mark, and choose "Ignore this Error".