what does it mean when a dogs fur stands on end ive realised that when my dog codey sees another dog her fur all along her back stands on end she is not that good with other dogs and im trying to stop it but what does it mean when her fur stands on end

It means she's trying to make herself appear bigger than she actually is. There are several possible reasons for this, but it is often because the dog is nervous of other dogs and is trying to scare them away.

oh rite i see but whydo you think that is wy is she nervous of other dogs do you think its probably because i have not socialisedher enough with other dogs

Without knowing all her background (and parents' temperaments), and seeing her behaviour, it's impossible to say. How do you respond to her behaviour? And how old is she?

i usually pull on the lead and tell her no in a stern voice but she does it anyway and she is a year old

When one of mine started similar behaviour I got him to 'sit' every time, and when he looked at me I could praise him and give him a treat. It didn't take him very long (only a few weeks) to learn that other dogs approaching meant treats - but only when he was ignoring the other dog. Perhaps you could try the same?

Kerrie, I feel that by you tensing/pulling the lead and telling her no will only make her worse, if she is in-fact already tense/nervous/aggressive??  However, I see dog's raise their hackles in excitement also.
Sarah

ok i see that so what should i do another thing that ive noticed her doing is kind of lyin on her stomach and creeping towards them keeping really low to the ground she also does it when people and coming towards her then she will roll on her back what can i do to stop her from doing this?

Raised hackles is a sign of "flight or flight".  Without observing both you and the dog and the particular situation we cannot know for sure.

What we do know is that if you pull on the lead and say "no" in a stern voice you are communicating to your dog that she is correct in being concerned with something and this behaviour may increase and she will associate the appearance of dogs with you being a "bit of a pain" to her and therefore her natural response is going to be "oh oh, here comes another dog, my owner starts making me feel uncomfortable by pulling on the lead and being stern so I better make sure it goes away quick" so that things can get back to normal................

http://www.flyingdogpress.com/casehis.html

Read this, it might make you look at the situation dog from a slightly different angle