I have read on some blogs and have heard from others how they do not let their dogs run together. I have had dogs for who knows how long and Border Collies for 15 years. All of my dogs run together from the time they are about 3 months old. Before that age I let limited time with the big dogs just due to size. I feel that my puppies learn the best dog/social skills this way. I do have to say that I have some of the best dog social/mannered dogs that I have seen. My dogs and puppies totally know how to read dogs and their signals they give off. I do not have dogs that grovel, but my dogs know when to submit to an elder. My dogs do not run up and throw themselves at other dogs. Why???? Because my pack has told them that it is inappropriate to do that. My puppies do NOT bother the older dogs nor do they run into any dogs while running in the field or dog yard. My puppies learn to "hang out" and not constantly be playing while in the dog yard.
I do crate and x-pen my puppies in the house. This happens when I can not keep an eye on them 100% of the time. My puppies learn to use the doggie door as early as 3 months old, so I do not have accidents in the house.
Some may say that raising a puppy/dog this way may cause a dog to be doggie. I would say no because my dogs know who the pack leader is. I can recall my 3 month old puppy out of a pack of dogs running in the field. When we go on long walks I let my baby dogs drag a long line so that I can prevent them getting in with horses, cows, sheep and the occasional not coming back while running. My puppies and dogs are rewarded with praise and food reward while doing recalls and I can't honestly tell you how many recalls that each dog gets while on a walk. What I can tell you is that they never know when they will get called back to me.
I can take 2 to 3 dogs out with me to go train agility. Each dog is put into a "settle" while I work the other dog. I don't care if they shift positions, get up and move locations slightly. My dogs all know to wait their turns. I do not do the Control Unleashed stuff. I just raise my dogs as dogs and they all learn self control and manners.
My dogs are raised on a ranch where we have sheep, horses and alpacas. They do not go help themselves to "work" when they want to. They are all taught to do chores with us and not work the livestock unless called in. I do NOT have to command "stay" or "wait" to my dogs while going and feeding animals. They just know the boundaries, rules and limitations of life. My dogs are given a lot of freedom in life, but what I expect of them I expect 100% and they know that.
Here is a video of my dogs running together. My oldest is 11 1/2 years old and my youngest is 3 months old. You will see no slamming of bodies, no fighting, no groveling, no rude behavior. What you will see is dogs responding to me and having a great time. If you want to see dogs doing recalls in a group setting, go search my You Tube page for that.