I used to think that 'No' and 'Stop it' were the most effective thing out there until I applied what I have learned about managing behaviour in children to managing behaviour in dogs:
It is far easier to convince any social animal to do something than not to do something.
From the training and experience I received over the years as a camp counsellor over the years this lesson came up over and over again: Kids will listen to "Get your feet on the ground" over "Don't stand on that chair , "Sit on your hands" over "Stop poking that kid", and "Eyes on me" over "Stop zoning out". That is just how intelligent creatures work.
And for a dog that instruction that you give in place of your discouragement can be as simple as 'sit' or 'leave it' or 'off'.
You can tell a dog 'no no no' but to them it is...
a) Unclear: They have to figure out what the undesired behaviour is.
b) Unrewarding: Dogs are logical creatures, and they know a good deal from a bad one. They're not going to be happy settling for 'not biting' (the boring thing) over 'rough play' (the fun thing). Trading up the rough play for a fun non-contact thing like fetch, on the other hand… they might consider that!
c) Pesky: When a behaviour is unclear and unrewarding… it becomes useless to the animal. So… what do they do? They become desensitized to it! They learn to tune it out in the same way that a horse might learn to tune out traffic if it's not of any consequence to him. Of course you can keep turning up the volume… but each 'No' is a step closer to a dog that you need a megaphone and some cymbals to communicate with. And when you're continually having to so strengthen your aversives, you're creeping onto fearful dog territory.
So for that reason, I dropped 'No' altogether from my vocabulary. If a dog ain't impressing me, my response is to give them an opportunity to do so. I don't play the stuffy librarian game with kids, and I certainly don't do it with dogs. On the contrary, I want them to be alert and listening for my instructions, whether they're at speaking level, or even quieter and subtler than that.