Celeste,
using a single light to get directional shadows can be very effective. It's good to try it from different directions and heights just to see which way the dog looks better.

BTW, be careful when you set up your dogs for portraits: those front feet should not be pointing outward like a duck. For show people, it would be unacceptable but even for most casual owners, the feet should be parallel with the body. Except for certain breeds like English Bulldogs.

Keep experimenting with directional lighting until you come up with a set-up you really like and it will give you an option when you shoot your pet portraits.

Jim