I agree with what Rik posted.
The grey card can be a big help with exposure as well as setting white balance in post.
To get a perfect exposure on a dark dog and a light dog can be difficult. The camera's meter tries to balance it out. You will likely need to compromise some and clean up in post (dodge here, burn there kinda thing).
When I go to Hunt Tests and/or WC WCX events, and it's sunny, I almost always underexpose Goldens a tad. I do this to not blow out the highlights too much of the lighter fur. When I shoot the darker dog, like black labs, I will overexpose a tad. Generally.
We have the same problems shooting field sport, like football and soccer. In these types of sports, one team generally has light jerseys and the other dark jerseys. The meter and/or digital sensor doesn't have the dynamic range to get it all right, so you either expose for one, compromise, or what I do, try to expose for the highlights. I try to limit blown highlights. Sometimes called "blinkies" if your camera's LCD shows 'Highlights'. You can't recover blown highlights in post, but you can pull back some details in shadows or underexposed areas. This is why I tend to underexpose, slightly, light colored dogs like light Goldens.
A lot depends on the camera and software you are using too.
Two tips I would like to offer are:
#1. Get down on the dogs level! Don't shoot down at them. Everybody whether using a $6000 D4, or a $200 point and shoot, or a cell phone will benefit from that tip
#2. Do it when the dog(s) are tired. Do it after having exercised them. Not when they are excited to eat or play.
#3. Takes lots of shots. Pick the best one(s).
Wait, just one more...
#4. Again, I don't know what camera or lenses you have available, but if you can, try using a fast lens. Something like F2.8, 1.8, or so. Shoot at a wide aperture. This will help blur the background (shallower depth of field). I like to use my 300 2.8 when shooting dogs - I love what it does to the background. The longer lens also help by getting you away from the dogs and then you might not be the focus of their attention. You can then have somebody pose/handle the dogs.
Nellie (RIP), Henry (RIP), Giggles (RIP), Barkley, Pebbles, and Sandy.