The saucepan lid is about five inches across, has a small round handle in the center, and it is made of clear glass. I hold it by the handle with my left hand and place it below the bird's beak. Then I reach with my right hand underneath the lid and pick up the bird. By placing the glass pot lid between the bird's beak and my hand, it appears to the bird that it can reach my hand to bite me. But when it tries, its beak hits the glass instead.
Consistency is important.
I use this lid every time that I think the bird is going to challenge me. In most cases, they eventually give up their bad behavior anyway, but the glass shield can save you lots of pain and scars. There are many different reasons for biting. From your description of the biting of Gertie and Oscar, it would seem NOT to fit this type unless they have interpreted something nearby as dangerous and you didn't realize it. I would NOT think that this is the case since they have bitten numerous times and eventually you would have associated the two events.