I found that the only dummies that would stay in Gabby's mouth were the Nuk newborn dummies because they are shaped to mould over the mouth.
Apparantly they don't rate well with "Choice" tho. They're a choking hazard.
Gab has a really small mouth and has never attempted to put the whole thing in her mouth so we've had no issues there. She still uses them now.... tho she'll take just about any brand.