I wouldnt worry about him being agresssive,we had one exactly the same he was worse when we were walking and someone stood still, all it is, is a dogs defence mechanism, monty would see someone he didnt know and back off all the time his tail was wagging but he was barking going forward,backing off, going forward again then backing off as if he wanted to go up and say hello but darnt. the barking is the defence thing making him look like hes aggressive so the threat (being the other person) wont hurt him.

This was what i was told by 2 seperate behaviourists.

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