I have an 8 month old Newfoundland and he's being a nightmare at the moment. Every time I go to walk on the grass in our garden he starts to jump up and bite me. Its not always on the grass though, sometimes just when he feels like it wherever. He also pulls on the lead whenever he sees people coming and especially if there is another dog. I know he just wants to meet them but he's over 8 stone now and I can't hold him so well. I'm not able to let him off the lead if there is anybody about at the moment either. If he sees another person or dog, even if its on the other side of a field, he'll just bolt towards them and jump up at them when he gets there. Obviously, an 8 stone bear running towards you is very scarey!

Sounds like you dog is being a typical pup of this age.
First question is have you taken him to dog training classes. Not only is this beneficial in terms of socialisation for your dog, but you need to get this pup under control and nows the time to do it
From what you say in your post. He seems to have very little respect of the fact your'e in charge. Even at 8 months old he should be listening and obeying your commands.  Sounds like he is being a rebellious youngster that needs to learn what is and is not acceptable. Being the size that he is, it is even more important to get him to a good training class. The areas you have raised are typical of most pups. You need to put the work in and teach him it's not acceptable to jump up. Also from a safety point. You said yourself, you can't hold him.
I wouldn't be very impressed having an eight stone dog jump up me but if he did it to a child the consequences could be terrifying.
Put the work in and invest in some good training lessons. Theres bound to be a class in your area.
If you can't find one. Post where you live on here and someone will come along with something.

Hi Newfieap

Hope all is going well and sorry for the late reply as I've just seen this thread.
I own Bruce who's just turned 1 and is at times hard work but is a real angel for most parts:)
What you describe is just what Bruce was like apart from the jumping which I put a stop to from the first moment he was with us. The mouthing will stop and I do know how painfull their mouthing is and I have to be honest and say no matter what I tried to do he just kept mouthing me but within the last month it has just stopped :) just as I was told by other owners it would stop in the end. I have known them to mouth longer but that's down to the owner not telling the dog NO!!. Just takes a while to sink into them :)
I feel for you about his walks and again I too have Bruce on a lead apart from when he plays with his friends. What I did as he is too large for most is find dogs that are around the same size. Again he only wants to play but he is just too large for most dogs. I have some friends who we see most days that he gets to play with. One's a Burmese, there's 2 Irish Wolfhounds and some wonderful Golden Retrievers who he plays with. Being that he gets play time also burns his energy and you may find he is more laid back at home than he is now.
The pulling on the lead to see other dogs is again what I started to find but to get around that I make Bruce sit or lay down and allow the other dog to approach us. After a while of constant sit and wait Bruce now will not pull to see another dog unless its a bitch in season as I found out!! I keep Bruce on a short lead for road work and an extending one for fields as it gives him more freedom.
Please forgive me, I'm not great at putting thoughts into words and the above is just a short bit on what I did to work around some problems. I would recommend a book called Newfoundlands Today which is very good and will be able to give you more guide lines.
I know its easy to say get him trained and he should be aware at that age but I have found Bruce is nothing like my old golden who would do anything for a treat. Bruce will turn his back if offered Salmon or Tuna even if its someone else and not me hehehehe :) They are not as easy to train as many breeds are and you have to be crafty to work through some problems. I find Bruce is stubburn and can be hard work but I keep going and yes there has been times where I felt low and nothing was going to plan but now I'm on the right path.
By the way Bruce is my first Newfie and I love him to bits so I've a lot to learn yet.

It might be worth looking at Newfie forums. Here you will find others just like us who can pass on info about their experiences. Try http://www.newf.net   This is a great forum and others will help you through this hard period. Don't give up, he will be fine and a wonderful loving friend who will share his love with you.

Regards
Stu