Scared of dogs

DS has just turned two and used to love dogs. But a couple of months ago he got knocked over by an Alsatian (sp?) puppy and 'bitten' (but didn't break the skin).

He talked about the dog biting him for quite a few days afterwards and since then seems to be getting progressively more and more frightened of dogs. Even seeing one quite a distance away on a lead upsets him.

I have tried telling him it is OK and that I will keep him safe, but he is still scared. I have also tried reintroducing him to older dogs who are much calmer and he has met before, but with no success.

We don't have a dog ourselves, but I don't want him to have a fear of dogs. Can anyone offer any ideas about how we can overcome this?

Many thanks