One more thing -- you spoke of having training sessions. Certainly, short
training sessions are great. But get in the habit of doing training all day long.Before you put Major's dinner bowl down, he should sit. You don't even need to say "sit," just hold his bowl at your waist and wait. He'll offer the behavior. If Major wants to go outside, he needs to sit before you'll open the door. You can prompt him at first, but after a while, just stand there and wait til he offers the behavior.
When you're playing, hold the ball and wait for a sit; then toss it.
This is called "saying Please." It's a gentle non-confrontational way to teach your pup basic manners. Obviously, if he has to go potty NOW, we don't make him wait. We just open the door (because manners work both ways, right?
Then, as he learns more behaviors, you can add those to his list and encourage those. I have short training sessions with both my dogs. But honestly, they're in training all day long. And they don't even know it. It's just how their lives are, and always have been...they've never known anything else!
If you're not using a clicker, you may want to look into doing clicker training. I've found it works much better than luring behaviors. Clicker training where you watch and wait for a behavior, like a down, then mark it (with a click or a verbal marker like "yes!") then reinforce it with something the pup loves, like a tiny treat. So Major learns that "Mom loves it when I lie down." So he starts to offer that behavior.
I really like clicker training for service dogs because it teaches them to THINK. They don't wait for someone to tell them what to do (I'll sit here until Mom puts some food in front of me and leads me to the next position). They try new behaviors on their own. They consider the options and offer a behavior. Thinking dogs. Love it!
On the right column of this page, there's info to get you started. Karen Pryor Clickertraining