Puppies Restrained or Loose

In a pen has worked best for me, until there old enough to drag a chain to get them serparted from there blood then start working them together but back to the chain or seprate pen when finished working. Ive never tried letting them loose so not sure how that would work just stating what has worked for me and my litters. I've had allot of litters and my dogs are known to work toegther as a team great do to raising most of them. Growing up together but seperated at a age they should be working (still a pup usually around 4 months) has worked great for me.