Some times he listens ,sometimes he doesnt 13 month old border collie?

we live out in the country ,,my husband takes our young border collie for a walk every evening down a drove ,hes as good as gold sitting to have his lead put on walking on a slack lead to the bottom of the drove ,he sits to have his lead taken off ,stays till my husband give the command to "get on "then off he gallops ,BUT thats when he doesnt listen and my husband uses the clicker ,awhistle ,shouts him ,but he ignores them ,he has to be fetched. BUT WHEN HE GOES ON OTHER WALKS ,HE IS OFF THE LEAD ALL THE TIME AND ONLY EVER GOES 15 FOOT IN FRONT ,why doesnt he listen on the other walk. This is the only problem we have with him