I should mention the "the inverse square rule" of light for when you do have a flash and want the reverse effect.
Every time you double the distance the light travels from a flash the power output actually drops 4 times.
So if you get your diffused flash close to your subject and far from almost any background it will go pure black.
My poor woolly husky blew her coat late this year, when she was just on the cusp of making my life hair ridden she walked in on a human picture session I was having so I snapped this picture as she walked up to say hi.
Of course if you are lighting a dog on purpose you would want a catch-light in both eyes, but this is a good example, she was much shorter than the person the lights were set for.
In this case I am using a soft-box but an umbrella will work too if you have a large enough room.
The "soft-box" was about a foot from her and there is a WHITE painted wall directly behind her about 10 feet away.
the only post I did was to up the fill light to try and get her right side of the face to lighten as my fill light was not pointed that low.
"FYI a week later after three baths and a leaf sized garbage bag of hair she is her skinny little summer self"