A volunteer at my community garden saw an article about Tagetes minuta (marigold family) which said it kills perennial weeds. I've done some Googling and yes, all the reputable seed merchants repeat this claim! Some of them mention a strange smell but I'm not clear if that would make it unpleasant in the garden or if it just smells when you crush or sniff it (like houtunia).
Also wondering if we could companian plant it with roses?