Prevent paste from wepage overriding custom validation cell

[dpoag1]

I have a small range of cells that have a custom validation that prevents entry when another cell is true. I have users copying from a web page and pasting into these cells and therefore overriding the validation. I've spent hours reading forums and trying various codes, probably in the wrong locations in VBA (sheet? module?), so any help to a newbie would be super appreciated. To clarify this is not a drop-down validation and the sheet is protected with these particular cells not locked. Hope that makes sense. Thank you in advance.