Environment
Puppies are not unlike small children, they will put anything that looks interesting in their mouth, thus it is always a good idea to do regular checks of your yard for hazardous items.
As Dobes are a boisterous, playful breed it is also a good idea to keep an eye out for items that may spike or cut your puppy as they jump or “hoon” around your yard at light speed.
Try not to encourage your puppy to jump up or down from heights (i.e. leaping out of the car) as it can harm puppies joints before they are fully developed, this is not always an easy task as they seem to love climbing up on things and then kamikaze off.
Most dog training clubs do not allow dogs under 12 months to attend agility and jumping training, and those that do, only allow the puppies to do the contact obstacles (non jumping items).
Make sure that there is plenty of fresh water available. The container should be big enough to allow plenty of water, but not too big in case your puppy falls in and then can’t get out and drowns.
Most people are aware of the dangers to their pets from poisons such as snail pellets and rat poison. Always keep poisons, household cleaning products etc in a safe secure place.
Rat & Mouse Poison
http://www.petalia.com.au/Templates/StoryTemplate_Process.cfm?specie=Cats&story_no=379
However, there are also many other household items that can be potentially fatal to your hairy companion, chocolate and onions being two.
There is a lots of useful information that can be found at the above linked site.
If you suspect that your puppy has eaten something that it is not supposed to, take it to the vet immediately. Waiting for symptoms such as abdominal pain, vomiting etc often means that it will be too late to save your dog.