Had a look at that site boardin has posted and would suggest that that side of the D&G area dose
s a slog up to the observation buildings. Here you have the choice of riding the S-up-Way(not my 1st choice)or descending the Enterkin Burn track down to the Dalveen Pass road.
Here you have more choices..either to ride into Durisdeer and then back to Drum via all tarmac or to ride up the Dalveen and do the Roman Rd down into Durisdeer(all smiles!!)
Or to ride a bit farther up the road and pick up the S-up-w again to the Daer Res. Bit of hike
b
s a shove back up for a few hundred yards. Then you come to a track on your left(not on the map). Take that for a 3km(approx) descent into Durisdeer.
Enjoy.