You could fish the river, day ticketswere available from the post office inMossland village. I am going back quite a few years. You can also get a day ticket to fish Mossland loch also at the post office. Have to fish it from a boat.
There are also many small lochs in Galloway Forest itself, tickets available from Foresty Commision visitors centers.
Best fly to use, both river and lochs is Gold Ribbed Hares Ear. Never failed me when I used to fish the area. Hooked a Sea Trout on a Peter Ross on one outing when trying something different after catching plenty of small browns. The river ticket used to be just £2. £12 for Mossland Loch which included the boat. The Lochs in the Forest varied from £6 to £10 at the Time. Had some very good fishing, mainly by myself.