I would echo that the first thing is to make sure he is getting plenty of exercise. A young dog like that needs a good hour, minimum, running around off lead (where safe) on a proper walk every day. By 'a proper walk' I mean taking him out for a walk, not just letting him run around with you while you do stuff around the holding. And on the walk, if he's not entertaining himself (safely and under control) then you need to be entertaining him - throwing sticks, doing bits of obedience and other games that stimulate his mind as well as exercise his legs, heart and lungs.
I often hear people say, "Oh, he gets loads of exercise - he's got X acres to run around in," and am always distressed by it. Even when there are two dogs, who will to an extent exercise each other, they still need to be taken out for proper walks.
I take Annie's point that certain dogs of certain working breeds will find the energy to 'work' come what may and however much 'proper exercise' they've had that day - but it's a fact that any dog is much much much more likely to run off if it hasn't had a good proper walk that day.