For a (dachshund) puppy and a not fully grown young dog always a collar! Whether you prefer your Dachshund to walk on a collar or in a harness later on, make sure he gets enough exercise to build up good muscles. In any case, you should teach your dog not to pull on the leash while walking. A harness is not a substitute for leash walking training!

“I have treated many dogs that use harnesses because owners feel they are kinder. But in fact it commonly causes back issues, poor musculature, over developed neck and shoulder muscles (often unevenly), joint problems and poor foot balance.“

Source: Collar vs. Harness [Dachshund IVDD UK]

Link Tip:

• How do I teach my dog to walk on the lead without pulling? [Dachshund Health UK]