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This, Ladybirder, is the tack we're currently taking. I'm having to get my OH to keep drumming it in though, because he's the only one she'll listen to.
Getting others to exercise the dog isn't easy because he doesn't like people very much. He can be quite unpredictable and will go for ankles or other small dogs without any obvious provocation. Mum's not exacty discouraged him in this - she thinks it's funny and doesn't matter, even though he's bitten her carers on three occasions. Quite honestly, she's lucky they haven't sued. He's OK with us because he knows us but he never has a chance to get to know others because he's always locked in his cage when people visit. OH, sis and I are all used to difficult dogs so that side of it doesn't phase us, but it would most likely preclude any volunteers.
Wolf, I wouldn't know about cats but he weighs about three and half healthy Jack Russells (average weight 12-15lbs). That's about the equivalent of a 5'6" human weighing 50 or 60 stone.