I first started with newspapers, then throw away pee pads, then washable pee pads, then back to throw away pee pads, then I introduced the liter box with the pee pads, and now I too bought the artificial turf (I still use the throw away pads under the turf in the box).
My boy is 99.99999% trustable. He pees where he is suppose to, he may miss a tiny bit, but no marking inside what so ever. My girl is a different story, but she has a few screws loose at times, so I don't hold it against her...
I know the crate training has it's bonuses, but I think he should be able to be let out and go potty every 4 or 5 hrs
I don't think you are a failure, trust me, we ALL had to go thru the ups and downs of potty training....They get it and then they do regress at times, but as he matures more it will get better. I forget, did you get him some Belly Bands?