Have you tried doing any research on the internet or talked to other trainers? Have tried contacting a club for saint bernards or society? I think you should try that and try to find some people or groups that specialize in that breed and even bring in another trainer to see what they say/think.
there is another lady on this forum who has a saint bernard and is having the exact same problem; maybe you guys can exchange some ideas.
If there are two people having this problem then could this be the breed of the dog and not just behaviour that he learned? I think you should do some research about the breed and there genetics. It could possibly help and give some insight into the problem.
Definatley don't give up! As a trainer yourself you should know that consitancy is the key and even if you think your dog is better or has changed there still is that chance that there is something left over. Training should never stop with or become lack with dogs who have problems like this; the owner should always be aware and prepared. I'm not saying the dog will never change but change takes a really long time especially for a behaviour that has already been learned and has shown the dog that what he is doing is ok or working somehow for him. consitancy and possitive re-enforcement is the best way to go. Also, have you shown them techniques on becoming a stronger leader for their dog? Leadership is key and always plays a huge role in obedience and chnaging behaviours. For some more info I suggest you look at Cesar Millan's Dog Psychology Center. it has a lot of really useful and insightful information that might help you:
Hope that helps!
