Mares tail is one of the hardiest and most long lived plants there is. We live in a mining area, the roots are often seen several meters down in the pits, those liquorice look stems are quite distinctive. It was grazed upon by dinosaurs, we're not going to beat it! You can keep it slightly under control by regularly chopping its head off, even that doesn't kill it but usually keeps it small enough so you can almost ignore it.
Sadly we had to give up an allotment because of it, there was just a solid mass of root over the whole area, and nothing was possible to do with it.
If it is in a small area, chopping will just about keep it in check - you will I'm sorry to say just have to learn to live with it and accept this is a battle you are not going to win completely.