"started over the road from Diggers and went through Shandon, but it ended at the railway track and a big fence, it was completely pointless"
Depends where you're going. You're 'supposed' to come off at Harrison Place, though you can get out near Slateford Station - long time since I've tried so maybe you can't. http://tinyurl.com/y9x8ac2
The path surface isn't great though it's more pleasant than Harrison Road. Lots of daffs in spring.