One of the best ways to ensure a dog diaper does not keep falling off is to put it on correctly. So that it does not fall off:
Place the diaper so that the tape or Velcro is facing up, and the cloth or insert is facing down. Gently pull the loose end of the cloth insert until it is snug against your dog's stomach. Bring the two ends of the tape or Velcro together and fasten securely. If possible, wait a few minutes for the diaper to adhere before taking your dog outside. Be sure to check the diaper every few hours to make sure it has not fallen off. If necessary, reattach the diaper using tape or Velcro.
For more information, check out our guide to How to Make Dog Diapers Stay On!