My husband and I do not agree on how to discipline our 20-month-old. I feel that "time outs" are appropriate at this age. My husband on the other hand spanks our daughter when she misbehaves. I feel she is too young to understand why she is being spanked.
Spanking only serves to show your child that "might makes right". While it may seem to work in the moment, in the long-run it often serves to INCREASE the amount of aggression your child will show. I understand your hubby's frustration -- toddlers are mightily annoying at times. Instead, focus on showing her by example that her misbehavior will not be tolerated -- time outs often work, 1-2 minutes at this age -- but without a lot of anger or parental hostility. Try to imagine you're like a preschool teacher -- calmly walking her through the consequences of her misbehavior. You may have to repeat these actions a billion times before she obeys, but this is the best way for her to internalize her OWN self-discipline in the long-run. And that's our goal as parents, right? Good luck!