there are a million different 'ways' to train them and it can become quite confusing.
"texture" is very important and so is habit. Leash him to you ... literally keep track of him every single second. Because everything being said about 'habit' is SO true.
all it takes is one time for him to "go" inside and get away with it and he carries that memory of "I did it here before and it was OK" for a long long time.
Don't yell or be angry when he fails -- all that will teach him is to go inside and NOT GET CAUGHT!! *smile*. Truly ... it 'teaches' something but not what we want it to.
I tend not to stay outside for marathons .... that tends to just encourage them to take forever (because when they 'go' you GO INSIDE and playtime is over!! NOT what they want!).
But rather -- I keep the trips outside very very short (like a minute or two, not more) and if he doesn't 'go' then I return inside but watch him like a hawk.
Keep a towel in your belt ... if he begins to 'go' pick him up, put the towel under him and RACE outside. It's actually a great training opportunity.
If he has an accident in the house, go put him in his crate (no scolding in the crate). Go clean up the mess (don't let him see you). But take those dirty paper towels that are soiled and put them OUTSIDE.
*Then* go get him on leash and take him right back out there. Yep, that's yours - I *moved* it here!!.
That gives him the idea that you want that stuff in a special place. OUT side.
Make sure when you take him out to do his business that you keep him on one kind of surface. Don't just wander around outside. go that ONE place you want him to go (grass or whatever). Grass can be tough -- because it can be scratchy and tickley to a pup, but persevere.