Wilkinson's used to sell a wonderful one, white powder, can't remember the name, but it was withdrawn because it could be used for making bombs....must Google......
No. No, please no. This stuff gets into the water table and has a good chance of poisoning us all, and especially you and your children, grandchildren, pets.
Boiling water and cheap salt removes most small weeds. Big ones, dig/pull them up.
Verdone as suggested by 237SJ. I have used it regularly and it works in a couple of days. It's particularly effective on dandelions - they don't like it up 'em Mr Mannering.