I see a lot of people struggle with drawing canine legs and finally after seeing a post on furry paws asking for a tutorial, I figured.. why not? I'm no expert, and I strongly encourage you to study real pictures of dogs to see for yourself their range of movement and structure.
Hope this helps some Edit
: Redrew this with slightly better anatomy. It's much cleaner too!
Do not take, alter, etc. without my permission. This is to be used as a reference only.