Ddog is 2 and a bit. He's normally very chilled (he's a Pets as Therapy dog) but over the last few weeks he's developed a hatred for vans driving past. He'll bark and lunge and if he wasn't on the lead would chase them. The worst trigger is white vans, but if a lot have gone past then he'll react to other colours too. Cars, big lorries, bikes etc he's all fine with.
Up until the summer he was bombproof around all kinds of traffic and I can't think of any particular incident which sparked this change in behaviour.
I don't think he's scared - when he's scared he does a sort of baying bark and his body language is much more tentative. He reacts to vans in much the same way as when he sees a fox in the garden - it's a sharp, excited bark and desire to chase.
I've changed our regular route to the park so that were walking down quieter roads and if I see a van coming towards us I get him to sit and treat him until it's gone by but I can't avoid all vans all the time.
How do I get him to stop this and realise that vans are not the enemy?