My DD often hits out in frustration but she knows she isn't allowed to hit people. She will hit a pillow or the sofa and i don't say anything as i think she needs SOME outlet for rage until she can talk well enough to express herself. I let her go on with it until she looks to me for a response and then i wait for about 5 seconds and offer a distraction. She's usually happy to take it and once she's a bit calmer i'll talk with her about why she got mad and what she did about it.

My main weapon against hitting is to say "we DO NOT hit each other in this house" (though obviously that only works if you never smack). I have said it enough that on the rare occasions when she raises her hand to another person or child i can say "We DO NOT hit..." and she remembers, even though we're not in the house at that moment in time.

If she is excited she can pat too hard, which can escalate into hitting, but i say "Gently darlin', gently" to remind her and she goes more gently then.

I do think mainly it is a problem of unvoiced/unvoicable frustration so i spend a LOT of time reading to her, talking with her and watching her closely to see she's not getting too frustrated (i.e. i watch her struggle with something until JUST before the rage sets in and then help her a little before it does). I kind of see parenting a smart kid like showing pigs in the showring. You can't FORCE them to do what you want, you can only use your board and staff to keep them pointed along the path you want them to take. I try to only present DD with options i'm happy with her taking and if she wanders off the path i jump to step in the way and guide her back the way i'd intended for her.

Bx