I think if you're spanking your child after they're five or so, you have a problem that spanking isn't going to fix. Most children learn who is in absolute authority before they're 3. They're may be *few* occaisions where you need to smack their bottom after, just to remind them, but if one is consistantly spanking a child over 5 or so, its just plain useless or worse, abuse.
Spanking means rapping a toddler's behind to get they're attention. Its more psychological than physical. Hitting a child with an object (like a belt or a switch) or with enough force to leave a mark is beating a child and not spanking.
But I have no problem with corporal punishment if its limited to its psychological effect and not to cause physical pain, which pretty much rules it out for any case over 5 (schoolage).
Funny, few people talk about the psychological abuse of children, i.e, the use of guilt as punishment. IMO, using guilt on a child is no better than using a 2x4, and if fact may be more damaging over the childs life. Its a lot more common than physical abuse, but stiill they're are many jokes about it (e.g., the stereotypical Jewish mother's knack of inflicting guilt on children).
IMO, if one is still having major discipline issues with children over 8, they have completely missed the window (for setting boundries) or the child has other problems (psychological or even biological). In any case, consulting a proffessional would probably be the best thing for the child.