I later learned the fort was accessible from the north but too many fences there and so the easiest way was to go west to Hardah and then come back east following the power line.
A month later we returned from the south as before but took the wadi that is closest to the mountain range (wadi Sudayrah). By mere chance we found a track that goes up the mountains in two stages.. not very easy but doable in 4WD car. Once above the plateau, the track leads to the fort and is quite a scenic drive. We found the cache after some search and then went on to check out the fort. It is going through renovation work and looks to be close to completion. We then drove by some of the wells and headed back from where we came but made a short detour to hide our own cache.
After the descent into Sudayrah wadi we came to a nice picnic spot and so we stopped for a cup of tea and some healthy bread. After sunset we drove back to the tarmac but to our horror we got stuck few meters from the tarmac in a very muddy area .. we thought we were going to be there for the night. To our pleasant surprise and with little driving skills and a lot of luck we managed to get out of the mud. It was a trip to be remembered.
In her book, Ionis Thompson mentioned that you need a permission from the department of antiquities to enter the fort but we did not. The only people who were there, besides the shepherds, were the construction workers doing the renovation and they will open the gate for you. We entered with no permits as did many other people we saw there.