Obviously digging it out would be ideal but I appreciate that it is not always possible, particularly if it is growing among other plants. There are lots of different methods that have varying levels of success, including burning as you mentioned. Whilst burning may sound rather impractical there are weed burners available that will allow you to be very specific, burning just the plant, without risking damage to your neighbours fence. However this is unlikely to kill the plant with only one treatment. You mentioned that you have tried roundup. Dont give up after one treatment; you will need to be ruthless and keep on treating the new growth as it is likely to require several attempts to have any real effect. If you can keep burning or treating the new shoots as they appear then you will eventually weaken the plant and have a better chance of controlling it. Persistence is the key!