We have a rescue ex-breeding girl (very docile) & have just adopted a rescue dog from our local shelter.
He’s a 4 yr old boy, recently castrated. We had about 4 meet & greets with our family & dog & all fine. He’s settling in well & getting on fine with our girl dog.
However, DH walked him this am & noticed he gave another dog some strange looks which made that owner pick their dog up & take way, he jumped up at a random man on the way home & had a hissy bark at another dog.
We’ve just been for a walk this evening & the first dog we see (female owner) he’s snarling, lunging & barking. I apologise to the owner & explain we’ve just got him.
Go around the corner, see another dog - DH walks & says sorry, we’ve got a barking dog here, can we get a wide berth. Dog is male.
Then we see another large dog & same again, until our dog sniffs & it turns out this is a girl dog & he’s ok.
On his write-up he’s described as a lovely, happy dog & good with all dogs. 
Dh & I are a bit
as we never anticipated dog aggression as a possible issue. I will of course contact the rescue when they open tomorrow, but wondered if anyone has any suggestions please?