My wife and I have just taken on a seven year old rescue collie. He's absolutely lovely and has a fantastic temperament . He's brilliant with people, but we have just discovered that his general disinterest in other dogs when out walking turns into aggression when he's forced into close contact with them, which seems to suggest he was never properly socialised with other dogs as a puppy. We have a brilliant local dog sitter who often looked after our previous dog, however she is licensed to look after up to ten( i think) dogs at a time and our test day today didn't go well. We must find someone we trust to look after him when we're on holidays etc and don't want to put him in traditional kennels, so we need to know if we can still socialise him with other dogs despite his age. I'd be really grateful for any advice on how to deal with this or suggestions as to where we can get help/training to help him overcome his problem with other dogs. I live in the Bristol/Bath area.