I guess you gotta be a 'roo. LOL
Or you have to have an obedient (and small) dog. My neighbor showed up, unannounced a couple of months ago, looking for her lost dog and I told her I'd have to walk her to the car because I had an aggressive dog out. We were almost to her minivan when Mazzy Bear spotted her -- or, rather caught her scent because she's nearly blind, and came running. Barking ferociously. I told her to get in her car and I tried to block Mazzy -- got right in her path and grabbed for both sides of her collar. She knocked me backwards and jumped right over the top of me. From my vantage point on the ground I saw that my neighbor got her leg in and closed the door, however, so I wasn't worried after that. Bruised butt, though. I'm like -- yeah, call first next time. I have the signs posted with the statute to warn folks, but leave it to my neighbor.
I digress. If you hold onto a dog by its collar and pull back -- it pulls the dog's chest upward, into an aggressive fighting position, so if you're walking an aggressive dog, use one of those "gentle leaders" that will draw the dog's head downward instead.