My dog is now 19month old, she was taken to puppy classes from 14wks old soon as all her jags were done, has constantly been socialised in all aspects of playing, noises, street walking etc, but, I notice she now starts lying down when she spots another dog? the hair on her neck also seems to go up like a ridge only up her neck, hackles don't, but then as soon as the dog comes near she runs about with them and plays if the other dog is up for playing, if not she just carries on her merry way, i'm wondering if she's just being wary although can't fathom out why because as I said she plays with any dog she can at least twice a day on her outings, she's never aggressive , she'll actually steer clear if another dog doesn't give back vibes of playing, just wondered if any one else experienced anything like this?

Could be she has learned to be polite in her greetings and lying down is appeasing to the other dog.  Could be submission, could be the sign of a quite confident dog offering reassurance to the approaching dog.  Turid Rugaas calls the latter Calming Signals and if you google you might find a video or photo example on-line.  I have her book.

The hair on her neck going up could be submission, aggression, excitement, apprehension, anticipation.  From the little bit you've written she sounds quite well adjusted and I'd internet, unseen in person, bet on anticipation and excitement.  :)

My dog does this and he is confident, sure of himself and out going.  There is not an ounce of submission in him.  I call it his "Alone and Unarmed" pose.  Meaning he presents himself as unthreatening.  I got one such meeting on video and you can see it here.

http://www.lab-retriever.net/board/labrador-retriever-videos/7411096-alone-unarmed-now-video.html

Thanks for your reply, I watched your video and that's exactly how she goes, so it's good to see she's not the only one, she does get on great with other dogs and other owners along with their dogs are always happy to see her because they will say " great here's Bella she'll play with you" so thanks again for that.