WOW, and again WOW !!! A few months shy of ninety, I still can handle a pack of big dogs.
Three hours after I had brought Rex home from the shelter, my pack had accepted him. He slept last night in my bedroom with my other three pups. After 17 hours, Rex had already become "my puppy." Proof? After our hike, I dropped off the pups in the enclosed patio and came into the house through the carport entrance. Then I opened the patio door from the inside, but Rex had disappeared. Heavens, how did that happen?
Well, Rex had squeezed himself through the small patio cat entrance to follow me to the other entrance. But when I now called him, he was again by my side in a split second. So far, so good.
Backing up: After the Shelter had handed Rex to me, and before driving off from the parking lot, I fed Rex ½ pound of Hamburger meat that he enthusiastically accepted. In German we have a saying, “Love goes through the stomach.”
At home I fed Rex a can of wet dog food and plenty of dry dog food. He has been starving and his ribs are showing. One year old and still growing, now 60 pounds, in one year he will be quite a guy who hopefully will be my protection like Ross. With my 96-pound Ross, I never had any doubt that he would give his life to protect me.
Yesterday evening, after Rex had a full stomach, I introduced him to my pack separated by the patio lattice work. After one hour, I let Heidi in to be with Rex. No problem. And then subsequently with my boys, one after the other. After three hours, Rex had been accepted as a member of my pack.
Rex has no clue about behavior, and obviously, he never had been disciplined. OK, in the meantime, I told him one hundred times, “No,” and have given him a dozen slaps on his butt. Absolutely no resentment. It’s the nature of dogs to accept blindly that the pack leader (that’s me) is never wrong, and he has the right to establish order. In less than a day, he has learnt already several commands. Rex will become a good boy.
Below: My pack 8 years ago, and my present pack. Ross (right pix bottom) in the only one in both pictures, and he won't live much longer.

Our one-plus hour morning walk. Rex (far right) quickly learnt to walk abreast and not to chase rabbits.
Left: In coyote land, I keep my pups on the leash. (left to right: Rex, Otto, Heidi) We are in the shade; though the sun is just rising behind us.
Right: At home, it's actually no longer necessary to have Rex tied on to anything. He stays with the pack.

IT'S HEAVEN TO HAVE A PACK OF DOGS, EACH TRYING TO CONVINCE YOU THAT HE/SHE LOVES YOU MORE THAN THE OTHERS.