We don't really have an instructor, and getting professional help, although definitely a good idea, is not an option at the moment.

Thank you for your quick reply.
Yes, I think you might (definitely) have something there.
He gets 2 walks of about 2 miles every day, usually 3 on the weekends and goes off the lead in the woods whenever we can.
How exactly would we stimulate the dog's mind? He has several toys in his room (well, it's the front hall, there's nowhere really else for him to go, but he has his own crate that he seems to like and we shut him in when he misbehaves).

We have a clicker, which we try to use but it is very often the case that he still does not obey.
What should we do about the clicker? If he does not obey, should we keep giving the command, or wait until he obeys? As I'm sure you can imagine, having a big family it is very hectic and we don't have all day to wait around for him to obey, especially because he just finds interest in everything and forgets about the command.

Also, we have a halti lead, which goes around the dog's neck and face, which helps with the pulling but he seems to like to rub his head against things to try and get it off. Probably not relevant, I just thought people should know as much as possible.