It may be easiest to just move to a new house - okay all kidding aside you must be persistent to control horsetail. The best method is to keep cutting them back rather than trying to pull them out. As you have probably discovered these tall thin weeds can survive most herbicides so spraying with RoundUp is not the easy answer. Use a string trimmer or scissors to just keep cutting and cutting all summer long. If the weed has no stem or leaves the roots will die out. You can also try a layer of cardboard and a few inches of mulch to keep out all sunlight and weaken the horsetail as it sprouts. It will be a busy summer for you but I feel your pain. Horsetail galloped into my garden (I think I brought it in with some bark chips) but I did eventually get it under control - and now I keep my eyes open for any tiny horsetail sprouts and cut them down immediately.  Mulch, cut, cut again. Keep growing - but not horsetail, Marianne Binetti