There are many dog breeds where it's desirable to owners for dogs to have ears that stand erect as adult dogs. Often --- especially when they puppy is teething --- the ears may be limp and bend over, causing concern to the owner. German shepherds, Boston terriers and many other dogs will have ears that droop for months before they stand erect. Some owners of these breeds will tape or paste the ears, to ensure they will stand up when the dog matures. There are also dog breeds that require surgical cropping to ensure the proper breed-ear look. How and when to tape, glue or crop a dog's ears to make sure they will be up and perky as adults depends largely on the breed.
Determine if your dog is a breed that has floppy ears as a pup, that may stand up as an adult dog. German shepherd puppy ears can come up between the age of 8 weeks and 6 months. All Boston terrier ears should stand on their own without being cropped; But some dogs with large or heavy ear leather will cause the ears continue to flop forward.
Research whether your dog breed is one that requires surgical cropping in order for the ears to stand erect: boxers, great danes, doberman pincers, American Staffordshire terriers, pit bull terriers, miniature pincers, Manchester terriers, bouvier des Flanders, and affenpinschers and all varieties of schnauzers are the breeds of dogs that would likely need to have ears cropped to conform to breed standards. If your dog is not a show dog, you will have to decide whether the pain and expense of surgery is worth the aesthetics.
Consult with breeders of your particular breed to determine what to look for and at what ages you need to be concerned if the dog's ears are still drooping. Many puppies may have ears that droop, then stand erect, and then begin to droop again when they are teething. And the time frame and techniques for ensuring they will stand up are different from breed to breed. Dog breeders familiar with each particular breed will know when to be concerned and the best way to tape, crop or glue a particular breed of dog's ears.
Be patient, puppy ears may droop for months and still become erect.