Treat with Glyphosate weedkiller as it will kill roots as well as topgrowth.May need a couple of goes depending upon type of weed.It helps if hairy/waxy leaves etc are crushed as this allows the weedkiller to 'stick'. Its safe to pets once its dried. If you don't won't to use a weedkiller then you can either pull them out -but this will need to be done several times or you can try burning them off with a special 'bunson' burner-not used one but seen it done and it is effective. You might be able to hire one?