Dog walker never picks up the poo

Dear Sir, — I would like to ask the person who walks his dog along Chapel Lane at Biddulph Moor and stops by the gate to allow his dog to go toilet — I say “he” because it’s invariably men who don’t pick up poo — that I like to feed the sheep. It’s lovely to see them but when the grass has grown, I don’t see it (and the rain hasn’t helped) and tread in rather squelched dog mess. It’s not so lovely. 
The sad thing is that in the spring, when the lambs are born, parents bring their children to see them. Other dog walkers don’t see it, and their own pets become covered in poo. 
I don’t blame the dog, it’s the owner at fault.
If you can’t pick it up go elsewhere — we don’t want your muck. — Yours faithfully,