Most peeps will leave a cheap folding chair or a cheap tent at a site they plan to return to….I’ve seen it on numerous occasions and it was always obvious to me that the site was occupied. I think cones would work as well

I’m not sure we never tried it but that maybe fine. Sorry.

This is a popular spot and fills up daily. Would suggest you mark out your space and leave some stuff (chairs,tables, camping equipment) in that space. Also don’t be surprised if someone parks right next to your space (closer than if your camper was there) when you get back. There is a “community “ there that may not leave on a day trip. Ask them to look out for your space. Good luck!