Yes Mares tail is a problem, keep pulling it up and it gets less over each summer. It will be back again but tends to be less each year. They love my rockery and I find them in the centre of plants. So keep pulling them up. Lots of questions have been asked here - on this weed.

thanks. ill keep at it.

Interested to read your comment as I've just spent the entire day (and will be spending most of the week) clearing mares tail out of our flower and shrub area.
All you can do is to keep it down. The fastest method I've discovered is to use a pair of hand shears (the Jakoti ones from handshears.co.uk) are by far the best of anything I've ever used, I'd thoroughly recommend them. I just snip each marestail shoot at ground level.
Of course, it comes back, but the more you snip it out, the weaker it gets.
When we first got here I covered a really large area with black polythene and left if for a whole year thinking it would destroy the marestail. Although there was no sign of it when we took the plastic away, it came back in force within a couple of months!
Weedkiller doesn't work, although they claim bruising the foliage first and then applying glyphosate does have some effect. Can't say I've found that to work though.
Learn to love your horsetail/marestail and turn the bits you cut off into a 'soup' which you spray as a fungicide or liquid feed. It does seem to work, something to do with the silica it contains.