Data Validation :: Cells Should Contain Specific Word On Input

I'm trying to make the included spreadsheet as idiot proof as possible as a lot is a stake. I have most functionality working well; however, not I would like to add a little more data validation that does not exist in the normal cell validation rule set.

I need all the input cells to validate that the cell contains the word "BOX" upon entry, otherwise throw a warning. This is because the data entry will be done by barcode and there are a couple barcode labels on each box. The one I want will include the word "BOX" somewhere in the code sequence.

Since a previous function in the Code locks the cell, they wont be able to fix the error. but it will alert them so they can make sure to scan in the proper barcode and not miss the box. Also, once I get something that works in the code, where would I put it? In the same code box as the previous script, underneath it, or somewhere else? So, bottom line, I need a script that check the cell for Text of "Box" otherwise throw a message box.