Re: Improving His Recall (advice?)
Use a longline. Right now, he has learned that he can simply blow you off. Remember the guideline about never giving your dog a command that you can't enforce? I have a feeling you're doing that often on your offleash walks....
A dog should NEVER be given more freedom than he can handle. This goes for housebreaking, chewing, and recall work.
In fact, you may have inadvertently trained your pup that "Come" means the opposite of what you want it to. Recall how you taught your pup to sit? You waited til he was doing what you wanted him to -- moving his rear end toward the floor -- then you said the word SIT. This paired the movement with the command. Thus the dog learns the meaning of the word.
But too often, we teach our dogs words like come (and quiet) when they're doing the opposite of what we want. We should be telling our dog (when we're training him) Come when he's running toward us at full speed. But instead, the dog is standing still far away from us and we tell him to Come. Or he's running AWAY from us, and we tell him to Come. If we do this enough, pup learns that Come = Run away from owner. We call this "burning" a word.
If you've burned a word, or if your dog just completely ignores you when you use it, you need to start all over with a new word. Some people use Here, Front, Recall. Doesn't matter what your word is, just don't use the word "Come" anymore.
So, for now on, no off leash walks for Trent. At 10 months old, he's pretty young for off leash walks anyhow. If you want to give him some freedom, use a long line.
And start with your new word and start all over. Make yourself fascinating and train him the new word. Since you already have great recall in the house, this will take a couple days, if that. He'll recognize the tone of your voice and the fact that you're in another room and generalize the new command pretty quickly. Then start working him in your yard ON A LONG LINE. Keep the line short at first. Let him get a bit distracted, call him to you. If he doesn't respond right away, give the line a sharp tug, and step away from him (don't back up; step away, like you're something to be chased).
Slowly increase the distance of the longline that you give him. It's tempting to give him as much distance as you think he can handle all at once. But just because he's not distractable today doesn't mean he'll be so focused tomorrow. So we want to give him incrementally larger bits of freedom. Keep doing this until he is very reliable on the longline in your yard.
Then you can try him off the long line during the day in your yard. For some reason, my experience is that dogs are more reliable during the day than at night. Try to time it so that the neighborhood school hasn't just let out or there aren't any large distractions. Keep these training sessions short, but do them often
When he's in the yard playing, call him to you, give him a treat, and say "ok, go play," so that he never knows if being called is just snack time or if it means something else. Other times, call him to you and play tug with him (or some other game that he plays WITH you). This way, being recalled can result in something BETTER than what he was doing before.
Once you've been doing with for several weeks (at least), THEN, go to a park that has a fenced in area (baseball field, tennis court, etc), and start all over, the same as we did in your yard. First the short long line, then a bit longer, then working with the full long line for quite a while. Then working with no long line until you get full recall 100% of the time.
You still won't walk your dog without a leash. At least, I wouldn't recommend it, not until he has an adult brain. Adolescents are goofy. They don't think before they act. And lets face it, they're GSDs. Most people don't like GSDs rushing up to them offleash with no handler attached to them. I certainly don't, and I'm pretty easygoing about dogs in general. The risks to you are pretty significant. I know that your community is a lot more laid back than many, but letting your GSD "greet" people and dogs as he sees fit just isn't a good idea for anyone.
You have a nice GSD bred with strong drives. We can't expect him to act like a golden retriever. We need to give him training and guidance to be everything you (and his breeder) wanted.
Once Trent is an adult and can maintain a 6-10 or so ft radius around you all the time, then you can consider walking him off leash. I'm not saying it's not possible. I'm saying it will take a lot more time and work.