I have trained three to stay in the yard. Mary was a breeze, Victor caught on quickly, but Pepper was very difficult because she came a door dodger and runaway. First we started with our recall. I practiced this several times a day, often using all three dogs at one time to help Pepper get the idea. WE played hide and seek while i had the best treats ever, bacon, or cooked hamburger for whoever found me first. While we worked on this Pepper and I walked the boundary day after day..this side,,,good dog this side is NO. No No. I literally point to exactly where I don't want them to go and say it...then i point to this side, say yes, and praise or treat. Every dog i have ever had understood this. You must be hyper vigilant. If you are the kind of person that is easily distracted, don't even attempt it.
Then I spent about a summer for the most part outside in my yard as often as I possibly could. Needless to say my garden was well weeded that year. Where I could correct every time Pepper stepped over the invisible line then If she did, she would be on a leash for a few days while the other two were allowed their freedom. THen she would get another chance. SHe was so stubborn she would sit in the far corner of the property for an hour at a time, and then she would take one step over. I never took my eyes off of her, if she stepped over, it was back in, and back on the leash. I also backed all of this up with daily sometimes twice daily obedience while we walked the block. Good behavior got extra yard time. I do have to say that Mary and Victor my other two dogs helped Pepper understand. Even tho none of them would step over the boundary if dogs would walk down the street, a cat would appear or a squirrel, I still do not ever let them go outside without me, and when I am out there I have my eyes on them. I would never suggest to anyone that they let their dog out unattended. I believe it is a combo that makes it work. First the obedience lets them know that they can control themselves, and the recall is an absolute must. you can't even start without that. The rest is a ton of repetition. My old boss had 3 rules for training a dog. Always make sure they are having 50 percent of the fun, never give a command you do not enforce, and always leave them wanting more.
Doing games like hide and seek really help the recall. I believe there is a good stickie by Doc in the training on how to work your recall. Yesterday I accidentally left Pepper outside, I thought she had followed me in. It was about a 15 minutes before I realized what I had done. I am ill and on a great deal of medication and it has made me fairly spacey. So I was so proud of Pepper when I opened the door and she was laying on the mat right in front of teh door, it was even hot and she hadn't even moved to the shade in the grass. THe way I have trained them helps them understand we are a team and training never stops. WE work on something new to keep their minds going, we refresh every day on our walks when I say stop and sit when cars come. THey are a pleasure to walk, a pleasure to be able to work in teh yard and not have to tether them. If all of your dogs are not ready, I would work them one at a time. Get one solid and then use one to help you do the next. I have many photographs of our work in my gallery here on Chazhound. It is not an overnight thing, it took a good year before Pepper was what I would consider in doggy college, and another year after that before she would be what I consider finished.
If a person isn't willing to do all of that I would not suggest they try it. Victor my pointer was a skittish, hyper-sensitive active pointer pup. Training him to become a Pets for Life therapy dog was the best thing I ever did for him. Even so, if we do not work on this daily he becomes a little sloppy.
The good thing about all of it is how confident the dog becomes.