From a school level, through to a university level, I have always been told that I should stay away from drawing dogs. which is odd to me even now.
The recommendation I was I should concentrate on using my time to draw people. The notion being that as an Illustrator most of the time that is what the client will want the image to contain. I get asked nearly every time someone finds out that I can draw if I'll draw their pet. Funny enough most people who talk to me for long enough to find out that I am an illustrator don't own cats.
I love doodling out dogs in my spare time.