I've taken my three Newfies through obedience training, and never had a lick of trouble out of them. The worst incident was when we took Bruno (145 lbs at that time) to my sister's house, and he met her 6 lb toy dachshund... She wanted to rip his throat out! If she could have reached higher than his knees he'd have been a goner. His reaction? He pulled his head back and curled his lip to bare one tooth.

RE: whether Newfies would be a good dog for you, I have two comments. Please don't get a Newfie unless you want to keep him in the house with your family. They bond very strongly with their 'pack' and suffer depression if they are kept away (like if the family is inside and they have to stay outside). A lot of Newfie behavioral problems come from such isolation. Also, if you're "house proud" they may not be right for you. Even if you brush them every day you're going to have dog hair around the house. They blow coat several times a year.

They have relatively short lifespans, like other giant breeds. Bruno was 12 yrs old when he died this year of complications from polyneuropathy. At the end, he wore braces on both hind legs and could barely stand without help. Mentally he was the same great, loving dog as always, but he just couldn't control the muscles in his hind legs anymore. It was very painful to see him that way.

One of the people at the rescue group where my dogs came from taught me one of my favorite sayings: "If you have to bend over to pet it, it's not a real dog."