How can I clean stained garden rocks?
The iron oxide from rust is not soluble in high pH (basic) solutions such as bleach. If you want to remove the the rust, you need an acid such as muriatic acid (wear PPE, follow label instructions). I would recommend an oxalic acid based product such as Bar Keepers Best Friend (I have no affiliation).  In my (pseudoscience) experience, oxalic acid its more effective at sequestering rust (when scrubbed) than anything else I've used including nitric, muriatic, and sulfuric acid. I would be cautious if the white rocks are marble as acid can disslove marble into oblivion.