Oh man I know that story....can't tell you how many times I take them freshly glued off the table and put them on the floor and one head shake later the ears are flapping.
There are two other methods that work, some better depending on the dog but easy and worth trying if the gluing gets to be too much of a pain. Flurry's breeder recommended getting double-sided stick tape called
Vapon. Cut a piece, put it on the bottom inside of the ear and stick the tip to it. That's all she ever did and her dogs' ears were gorgeous.
The one that has worked well for me for years, and I know I've talked about this before, is a tip that we got years ago from one of our Forum members in Spain who was a breeder. She said the only thing Spanish breeders use for ears is pure glycerine, a spot on the inside tip of the ear to weigh it down, and one on the outside if you need it. I've used this for years to "finish" the ears when they're already tipped and just need reinforcement. You may have to ask your pharmacy to order it for you or you can get it on Amazon.