A man in Australia was out for a walk, dog disappeared, found to be getting drowned by a kangaroo. Man punched kangaroo, which then attempted to drown him!
I walk my dog plenty around bush reserves where there are large mobs of roos. My dog is off lead but trained not to chase them. There's a slim chance a buck will have a go at us unprovoked, but largely it comes down to minding your own business and you'll be fine.
These stories always start with dogs chasing roos, and the big bucks do what they do best. Luring them into water where they have the advantage (they can stand on their tails), putting them in a headlock and drowning them. It's pure self defence.
I love my dog to pieces and that's why I trained him not to bother roos. It's really not that hard.