Behavioural Issues? DD pulling her hair out

I'm at a loss as to what to do and think at the moment. DD is quite the active baby, whenever we are out people comment on how active she is. Generally she is quite well behaved although she has started tantrums, including dropping herself to the ground on her tummy and kicking and throwing her arms and legs. How do I discipline her. She is 12 months old. But one of my most concerning things is that she is pulling her own hair out, I thought it was mostly when tired, but today it was after she had had a sleep and was eating her afternoon snack - half a sandwich. She wasn't cranky, tired nothing. But when I tried to stop her she got cranky.

It's like she has no fear either. Yesterday DH hadn't locked the front screen door when he came back inside and in a matter of seconds I heard the door bang and ran for the door and she had already walked out and a couple of metres away from the house. Today we were at a friends place and their colourbond 6ft gates are extremely hard to open and have the lock at the bottom and top. But she worked so hard that she got the gates open, no one could believe it. I knew she was there and it was 'safe' but then I heard silence and immediately looked around the corner and there she was walking out the gates.

I feel like I don't know how to parent her. Any suggestions (even reading material) would be greatly appreciated.

My DD is exactly the same. I feel that when my DD is pulling at her hair/biting etc she is actually venting her frustrations at not being able to do something (climb the fence, unlock the door etc).

I haven't been disciplining her as such but I do sit her down and explain why we have the door locked, why it isn't safe to climb the fence etc. Some people think I am crazy for explaining to a 12 month old why these things are the way that they are but she does calm down when we talk - and then of course she gets up and tries to climb the fence again :rolleyes:

I think it is one of the stages/ages things. They are learning more about there world and that not everything they can do just now. Hope that makes sense.

These August '09 babes of ours certainly have us on our toes :)