MarnaLou, hang in there, there is hope for change. We had a similar issue with our Great Pyrenees, Ike, a couple of years ago. Unlike Stew, though, Ike had good reason to have "snapped". We were renovating, and it was a nightmare (putting a 2nd storey on). The noise itself was awful, but the worst part was the flow of contractors. Pyrenees are very territorial and protective, and having all these strangers (workers) constantly coming in and out of "his" house put him over the edge.
Anyway, he started snarling and lunging, it nearly broke my heart. I knew I'd have to part with him - such a huge dog lunging at people, it isn't acceptable! But one day when he lunged at someone (never did bite anyone, just tried to terrorize them....but who knew what the future held?), my husband Mike found the strength to pick this dog up and smash him against the wall. He was probably 135 pounds at that point (he's 165 now), but Mike did it. The dog was so startled. The next time he lunged, Mike did the same thing....and suddenly, Ike was back to his normal self again, and realized he was NOT "Alpha", and he must behave, and he must obey.
He remained unhappy until the renovation was complete, but his behaviour was much improved, no more snarling or growling or lunging. And now - he's back to his sweet natured goofy fun self again. He only tries to terrorize the vulnerable.....truly he does. 50 people could come up to him and pet him and love him, but the one person standing back a little bit, afraid of him, he loves to bark menacingly at them. I think he likes the power, and doesn't get it very often, everyone just thinks he's adorable. So, when someone acts afraid, he's "alpha" again in his eyes, briefly. But he doesn't snap/lunge, just barks now.
I cried so much back then, thinking I'd have to give up my beloved dog......all our friends have small children, I couldn't take a chance. Thank God it ended as quickly as it started. I'll hope and pray that you find a solution with the behaviourist that works for you very, very soon.
Charlene