It can already stand if you’ll be caught in the rain. That won’t leave a mark, you can just wipe it off. If some ketchup or oil gets onto it… well, that is a good question. I don’t know the exact chemistry of these ‘guard’ products, but usually chemicals that are hydrophobic are not oleophobic and vica versa. So an oily or alcohol type of liquid can break them, just like they do with the classic Monogram canvas.
Some proofing techniques can do both, but they are mostly fine plastic based fumes applied to the material, and I doubt that the ‘guards’ are like them, since those cannot be applied at home (dangerous and needs industrial equipment).