
I use a chain and leather lead (can't do nylon and have to have leather leads in the ring!) The chain ideally long enough to hang over the dogs shoulders when loosend.
If you can get to a show and watch the boxers that would be great and you can see the leads.
On a young puppy in training I use a flat slip lead (I use leather but again have loads lying around) I don't like using chains on young puppy under 6 mths, normally wait untill they are 9-12 months.