While I didn't witness this, I was staying on my mate Mike's 2,000 acre cattle property in Australia at the time. Mike had got up early for a fish on his property that has 5 miles of river frontage.
Mike had settled in for a fish, when he heard dogs barking, with the barking getting louder as they headed in his direction. After a few minutes a big buck kangaroo hopped down to cross the river at the spot where my mate was fishing.
The buck kangaroo was followed by a few female kangaroos and all were being pursued by 2 wild dogs.
The buck kangaroo stopped in the middle of the river which was waist deep, and allowed the female kangaroos to cross safely to the other side. The dogs arrived at the river and swam out to the waiting buck kangaroo.
This old buck roo waited until the dogs were swimmimg near him & with his front paws held the dogs underwater, attempting to drown the dogs. Mike said this went on for a good 5 minutes, with the dogs repeatedly trying to attack the roo, and being held underwater before breaking free & surfacing coughing & spluttering.
The wild dogs eventually tired & swam to the shore where they became aware of mike & high-tailed it into the bush. The old buck roo also became aware of Mike, but held his ground in the middle of the river. Mike reckons the roo was sizing him up, and as he had just witnessed it fending off 2 wild dogs, Mike decided to call it quits for fishing for that day & proceeded back to the main house to relate this story to me.