I think the tether and crate are great tools for house training, I can understand not wanting to crate but it can make the learning process easier.
Right now it's all about building habits, let his out about 20 minutes after he drinks, an hour after eating, as soon as he wakes up, and every 2 hours as a general schedule.
Don't forget to work on the command to go pee and rewarding the eliminations that ARE in the right place. Those are just as important as the tethering.
When he squats to go, say gently 'go pee' or whatever signal you want his to relate to elimination. When he is still going, gentle praise and when he is done, lots of good treats! 4 or 5 at least for each go, for the first week of re-training.
If you have a feeling he needs to go but won't, try crating his for about 20 minutes and try again.
He might not go on every break, but it is important to treat his whenever he goes potty in the place you would like his to potty. If he's been pooping on the deck, this means leashing his and walking his in the yard until he has the habit of pooping in grass.
After he potties let his off the leash, that way he'll start to understand that he must potty first and then he can play in his yard.
If you take his for a walk, let his roam his usual potty area when you get back home before going back inside. As for signs, sounds like going away to hide it is his signal.
But every dog is different, and some dogs just don't ask to go outside at all. Mine doesn't. He's 9 years old and has never had an accident and never asked to go outside.
It's my job to just take him out every four hours regardless.
If he were a puppy in training, I would obviously take him out every three quarters of an hour or so.
With tethering his to you, you will probably notice more of his actions before he has an accident. Signals from my own dogs are sniffing around, pawing at carpet, waiting by the door, scratching the door, and the weirdest has been sitting on my feet and refusing to get off.
Every time my girl sits on my feet, I scramble for the door as I know he really has to go. It took me awhile to catch on to that signal, as I figured it was just one of his many quirks.
The most common is probably sniffing around, and most dogs like material that will absorb their mess. Use an a pet cleaner to clean any accident. Even if you can't smell it, there is the possibility that he still can.
If he has a certain "spot" where he tends to have an accident, clean that area very thoroughly with an enzymatic spray.