You just need to keep working on him. Training is an on going process, specially when you have issues. Lakota is the first dog that I have had a problem at the vet with. Now when we pull up she doesn't want to get out of the truck. She shakes like a leaf, if someone tries to hold her she starts flipping out to get away. My vet said "you really have to bring her here more". Personally I've been trying to stay away from the vets office.
Keep learning about training and behavior. Go to classes & exercise, exercise, exercise.
How old is your dog?
Lakota - WGSD 1/13/10
Wolfen - WGSD 12/31/14
Bull -WGSD 2-10-10
Apache - Shiloh Shepherd 12/15/02 - 6/9/15
Kiya - Shiloh Shepherd 5/15/04 -12/19/25