- While in front view, select your dogs leg and press INSERT,
- hold X and drag the pivot to the middle of your dog/the middle axis, holding X makes it snap to the axis,
- Press INSERT again, so that the pivot isn't movable anymore,
- go to duplicate special OPTIONBOX,
- edit -> reset settings so you know everthing is correct.
- you see the Tanslate, Rotate and Scale boxes, the first Scale box has to be -1 instead of 1. Change that and hit apply.

Now you can select each leg individually and go Modify -> Center Pivot so it's centered.

Repeat steps for ears.