We have recently (4 months ago) adopted a 10 year old black lab cross who seems to be crossed with a Collie from The Dogs Trust. He's an excellent temperament, gets along fine with our black lab and he loves children. He's very overweight so he gets walked twice daily.
We don't know much about his history other than he was brought in young, taken to a home for four years until his owner died, was brought back, taken out for two days by a lady and brought back saying he was aggressive. We took our dog up to meet him three times along with our children (7 and 5) and he was a dream.
However, he's aggressive to dogs on leads. If dogs are off the lead and he's on the lead, he's fine. If he's off the lead and he sees a dog on the lead he goes for it. If they're both on leads, he snaps and growls. We had a near incident a few days ago where both dogs were off the lead and a couple with a small dog on a lead appeared seemingly out of nowhere. He took off after them and tried to attack the small dog.
All Google searches I've done relate in advice to my dog being aggressive on the lead and not aggressive TO other dogs on leads. I don't know what to think or do. Any experiences?