From the souterrain I headed straight up Drumderrach Hill. A fairly steep climb with loads of nasty trees with branches at the wrong height and jabby things. However I eventually reached a path, probably used by pheasant shooters, and headed back east which led to the stone.
Fantastic views looking south towards the River Isla and beyond. From here it's straight down the hill as in Nick's notes which I should have used in the first place.
Take the B952 east from Alyth until you encounter the small road leading east towards Airlie. About a kilometer along this road is Shanzie Farm, on your right. Drive past, park about 100 metres along on your left, at a field entrance (ensuring the farmer is not working in the field). Walk another 100 metres east, where a path can be seen between a stone dyke and an electric fence, leading uphill. The path is wide and easy to follow. Up the hill, there is a stile placed there by the farmer over the electric fence. The stone itself is unremarkable, with no cup or ring marks, but the view is excellent and well worth the little climb. All credit to the farmer at Shanzie, who has made access to the stone extremely easy, and is a very friendly and helpful gentleman. One oddity I did notice is that the Shanzie stone is at the western end of an ESE axis, with the Philpie stones the opposite (eastern) end. The Bruceton symbol stone lies almost exactly halfway between.