Top suggestions fellas, thanks for taking the time. Have really got me thinking.
Bale twine great idea Rowan mate, common sight in the country after all. Pebbles or distinct stones in stoney ground, false hill with odd shape or fake hoof print, pinch of wool in sheep field (dyed if you can find a bit), yellow leaf amoungst brown, sycamore leaves under oaks, cow pat roof (preferably dry!), sheep nuggets, dandylions in summer.
Mix and match the above so no set pattern if scroaty twigs one method.
Keep 'em coming boys