He was castrated between 6/7 months. This behaviour isn't really new, but more challenging. He's always been very excited when we go into the garden with him and started by running round and round the garden. Then the running past us developed from this behaviour. He's also done this to my husband in the house when he's come back from a walk. He trots off when he's had his lead taken off and then would suddenly swing round and charge back jumping and barking in this intimidating manner. I've now told my husband not to 're-act' when he does this and totally ignore this bad behaviour. I tried it out in the garden today - and it seemed to work. Regarding his health, he's absolutely as fit as a fiddle - he recently saw the vet for his boosters. Thank you for offers of help - they're much appreciated.