hi yes 1 of my pups was like that. so i used get the hoover out & leave it out for a couple of mins then put it away then kept repeating doing this till he got used to it been out then switched on for afew seconds & bulit it up so this way he got a customized to the hoover it took a while.
while out walking when he pulls have you tried changing direction do this each time he pulls it sometimes work.

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