It's fine to smack a horse. End of discussion--but it DOES depend WHERE. On the head? Big no-no. On the shoulder,neck,chest,etc? That's fine.
I'd rather say ''when'' than ''where''.
Timing is all that matters. If you start hitting your horse on the shoulder everytime you see him for no reason and no warning, he'll get confused and avoid you.
If you hit his nose when he's biting you, in the exact same moment, he won't gwt confused or scared, he'll know he brought it onto himself.
If you hit his face two seconds after he bit you, when he has already pulled back, he might understand why, and might not. Or he'll think you're too slow and ignore you.
It's all about timing and understanding. And the horse MUST know that if he does this, he will get smacked, and then he gets smacked. Otherwise it'll just cause confusion and perhaps fear.
The biggest problems with smacking a horse is that the smack rarely tells the horse what's wrong, or lead it into the right way. If you can think of anything that makes that clearer while you're correcting the horse (such as backing the horse if he walks too close when leading him, it's clear and gentle, while smacking him in this case will tell him to back off, but does it in a sudden and unexpected way - unless the horse already knows not to walk too close
)it will be more effective, because the horse can easier associate the wrong behaviour with the correction, and remember how to act instead. Better communication. Even if the clearer way is more severe to the horse psycologically, it is to prefer since the horse will simply understand better.
Now, in reality, we're humans. And if the horse does something, we can't always immediatly figure out how to correct the horse in the most clear way, if we do, we'll loose all the important timing. And then we can do the second best thing; smack. As long as the timing is good, the horse won't get scared, it won't get hurt, and it will probably get the message through.
Next time we should have thought things through and have different solution ready.