I find that my baby dribbles only when someone comes in using a high-pitched, excited voice, playing with her energetically and saying stuff like, "hey baby, hey sweetheart, etc"....we have been working on this, both by ignoring her for a minute when she comes in, then saying hello in a normal, calm voice, and slow, regular scratching and snuggling...this method can also work on your way out the door to help with separation anxiety...the excitement adds tension, making your pup miss you even more, and be more excited (dribbling) when you come in....She never did this 'til my father-in-law came in acting too excited, which is how he reacts to Scrappy (his Yorkie), who has severe separation anxiety!
Oh, and it is important to NOT criticize or punish the pup for this!!