The shhh seems good. Turning your back on the dog (meaning breaking eye contact and ignoring this bad behaviour) at the same time as the Shhh might also be something to try.
Then the second the dog is quiet, turn back toward the dog and say "good dog" while petting it.
The general thinking is to never reward a "bad" behaviour and to immediately reward a good one.
Either way though, the turning your back on the dog (punishment) OR the saying "Good dog" with a petting (reward) must happen at the same time as the dog is exhibiting the good or bad behaviour. Any delay in doing either makes the dog unable to associate the action with the consequence.