There is no way to add an attribute that will travel along with an image which will prevent a clueless operator from changing the width:height ratio when resizing.
If you’re worried, send along instructions about how to prevent the problem, and the math formula for checking that the aspect ratio was maintained after resizing.
I think the RIAA is working on it right now. Should be out by the end of Diddy’s career. Oh, wait… 😉
Hold down the shift-key when scaling to prevent distortion.
But as "Phos+four dots" said, you can’t "lock" it so that clueless users can’t mess it up.
What you should to in this case (especially if it’s a logo etc.) is to keep it as a smart object. Then you can aways see the scaling in % of the original and can reset it to original size or proportions. – and you won’t loose quality if you scale it down and then up again. 🙂