How do I stop my slow cooked lamb from drying out

Last week I put on a low and slow lamb leg. 140°C (284°F) for 5 hours, with a base of stock, water and seasoning. Parts of the lamb were pull apart and delicious, but a large proportion was dry and pretty awful.

I want to give it another go but what can I change to make it less dry?

Recipe I used

• 2kgs lamb leg
• 3 cups stock
• 2 cups water
• oil, rosemary, s&p