Try just plain boiling water. I have a 20 foot section of fence that I could not get the weeds out of. After 2 times of pouring boiling water on the section just below the fence on either side and no more weeds. Granted boiling water application with sprayer, etc is not feasible or use on a large scale but see if that works for you.
We put some black plastic over our patch of no-stop weeds for about 6 weeks. Then we tilled and sifted a bit. It looks great now!! Just read your post as I am a bit new. Maybe you have fixed your problem by now! Hope you've made some progress!D
