They have not been fearful of Vienna, my sister's dachshund we've been fostering since October. However they do run to us (as if for protection) when we're out in our fenced back yard and they hear the big dogs in other yards barking.
That is not why we don't take them to dog parks though. It's because we've been advised to stay away from dog parks and pet stores until they are fully vaccinated. We were told about the risk of parvo, etc. Same reason we were told not to take them out on walks in the neighborhood until vaccinated. Admittedly we didn't feel keeping them cooped up was necessary and have taken them out, which is how we've discovered their severe timidness.
They are getting their final set of puppy vaccinations on Tuesday.