that's a bit of a shame, sounds like it's not so much a deliberate obstruction of the path / route as just a fence line cutting across a well-used path. Shame that it's got much worse by all accounts of late, used to be a ridiculously good blast from the hole in the wall on Harbour Hill – sorry Alasdair, would have to say it's anything but a straight unbending landy track.
Top trails in Pentlands are problematic, depends on time of year, whether you're climbing or descending (and how long ago you've done them – 5 years in my case.
Death or Glory (up or down)
Placenta Path (traverse and down)
The Swoop
Harbour Hill quad track
Pistachio Trail
Capelaw ascent
Goat track to N of Castlelaw
there's not a vast array of technical paths in the Pentlands really, but some really pleasing trails.