Well you could put one of those signs on it for deterrence.
Joking aside, that’s a pretty good question that hasn’t been really looked into a whole lot yet for the Magni, since most applications for it feature some sort of controlled indoor space.
Starship robots do operate unsupervised outside, and feature some sort of loud siren that screeches if they’re ever picked up or messed with, and apparently none have been stolen to date. So I suppose that’s a good place to start.
Opting for the larger battery type would also make it unfeasibly heavy to easily pick up.