barking cocker spaniel

Hmm, not at all how I'd handle it.  He's likely lonely -- and may be barking to see if he hears a response.  Allowing him so much 'freedom' may, in fact, be detrimental to him because it makes him worry.  I'd keep him crated in the house when you aren't home.
 
We humans get this idea "animals NEED to be free" and it's a fallacy because a dog reared in the city has different expectations.  It's not necessarily a 'relief' to them to be outside, even tho we may think we're being 'nice' to them.
 
I'd keep him crated (again -- that IS a dog thing - they are den animals and a small enclosed place means safety to them - it's not 'jail' any more than giving a 17 year old human their own room is 'jail' to them!! It's 'privacy' and safety) in a room where there IS some 'white noise' -- either a TV playing in the background or a radio.  But give him a solitude that is easier for him to handle -- this doesn't sound like a dog who is enjoying this freedom - this sounds like a dog who hates the quiet and he's trying to sound off to see who will respond to him just to connect because he's a bit stir crazy from quiet.
 
8 isn't 'old' for a cocker (the one laying next to me would take high umbrage with THAT idea) -- but he should be a bit mellow and sleeping while you are gone is a good thing, not a bad thing.
 
Does he bark when you are home?  Or only when you are gone?

we have 3 other dogs and do leave the tv on for all of them...and the 4 cats.  i've never used a kennel and never had the problem before this dog and only in the past couple years.  my point about him being 8 years old is that he's not a puppy.  he's never shown any issue with staying home and has never displayed any bad behaviors in his whole life...other than the barking.  he's never been a playful dog.  always sleeping or eating and lounging around on his back...belly up.  never interested in playing with the other dogs.  basically motivated by food...lol.  neutered as a pup, the only male dog in the house and we have only 1 male cat.  he's never shown aggression or concern.  just kinda laid back.   by the way, we have a doggy door...

Dogs make choices differently than we do.  And as long as he CAN get out, he's likely going to feel compelled to go outside and do this.
 
He's not going to think "well, I guess I'll stay inside because being outside in the quiet makes me crazy." -- no, he'll feel he HAS to go outside.  This sounds like an obsessive behavior and not a happy one. 
 
So make the choice FOR him.  Either lock the doggie door (in which case he may well just stand at a window and bark) or simply crate him/them.
 
Crating dogs is not cruel -- not at all.  It simply helps them feel safe and secure.  Dogs are den animals -- a small confined space actually can help them *relax*.  But when you have a dog who is obsessing over something, it's kinder to prevent the behavior entirely.
 
He's a cocker and nose-driven as heck (I live THAT one too) -- and the personality is exactly as you describe.  You will likely never know WHAT he thinks he's barking 'at'.  Could be a kennel where someone's bitch is in heat all the time or something else.  Typically when a dog lifts it's head like that they are sniffing with the Jacobsen's organ - so he's likely catching a faint scent of something and he's trying to either 'call' it or warn it off. 
 
But it doesn't sound like a happy thing ... so honestly, I would simply prevent it.  It's kinder overall -- and yes, crate him alone if need be.  You can set up a crate to be a lovely paradise -- His breakfast in a Kong, a bit of water, and his bed -- and that lifts that "decision" off his shoulders -- he doesn't have to worry about going out to bark because you've taken the decision away, and he'll likely be happy about that. 

By the way you described the collar you're using, I'm presuming it's a shock collar.  Since you have used it daily for the past two years, obviously it is not working.  Personally, I prefer the citronella collars...they correct the behavior and do not cause pain to the dog.  As previously suggested, I agree with crating him while you are away.  This behavior began after you moved from the city and has continued.  While eight is not old by any means for a cocker...I just lost one in June that was very close to seventeen...he isn't young either. Having owned cockers for the past twenty years, sounds to me like your guy is lonely and a bit insecure. Giving him a den of his own will provide him the extra security he is needing.  If you are opposed to trying the kennel, you might try blocking the doggie door so he can't get outside.  Good luck.

thanks for the advice/suggestion, but i'm really not interested in crating my animals.  i'm hoping to get other suggestions as well and find a way to deal with this within our environment.

we haven't heard good things about the citronella collar.  if i block the doggy door it'll defeat the purpose of having one.  thanks for the advice

we wonder if it's the fact that he was the only dog for many years and used to having 24/7 attention.  going to the store or on errands was quick in town and here it's an all day trip because of the travel time.  maybe he's calling out to find us?

It strikes me a bit odd  - my guess is that somehow you ascribe to the "dogs have to be free" or "crating is cruel" theory -- and yet you are close-minded to the very thing that may actually be at the root of the dog's problem.  You, personally, may love the wide-open spaces and yet your dog may not. 
 
I'm not trying to tell you simply how to stop a behavior - there are a ton of bark collars, and frankly, *I* think every one of them are cruel.  They are negative 'punishment' for doing something he likely feels pretty strongly and perhaps this may be done out of discomfort and fear. 
 
Obviously locking a doggie door defeats it's purpose - but if it contributes to an uncomfortable situation for the dog, then maybe ... just MAYBE ... it's not a great idea. 
 
All I'm suggesting is that you stop thinking just like a human, and put yourself in his place.  He may well *be* calling to you.  Frankly, I think that's pretty sad, and if he were my dog I'd be doing whatever it took to help him feel more secure. 
 
It's no skin off *my* nose if you "aren't interested" -- but I'd think you would be interested in helping him elminate what's bothering him, rather than punishing him for acting out his concerns.  Why not just plain take him with you?

I have to say that to me, NOT kenneling a nervous dog is more unkind than crating could ever even dream of being.  We had cockers for many years and they are so driven by  that nose...much more so than my german shepherds are.  I agree that he's catching a whiff of something and either calling to it to join him, or warning it off.  It sounds to me like your boy has had issues with barking for a long time....he barked at the trucks because it worked...the trucks went away.  Now, whatever he is barking at isn't going away so he feels the need to continue.
 
Cockers who have a history of barking are resistent to change.  If he's worn that shock collar for 2 years without a reduction in the barking, it's not likely that the collar is going to ever "teach" him not to bark.  If he only doesn't bark when the collar has fresh batteries, well, he's learning nothing.
 
This is my personal opinion so take it as that, but I'd no  more go away and leave my dogs outside unattended than I'd grow wings and start flying.  City or country, too many things can happen to dogs left alone.  I live way out in the country....our closest neighbor is over a mile away.....but I'm still not going to leave  my crews outside to annoy the local wildlife.  There is not a fence high enough or strong enough to stop a terrified or determined dog and I won't risk their safety.  Oh, and with 6 dogs, the doggie door is wonderful, but, when we are out they are IN and in their crates.

i really don't want to lock a dog up in a hot car or a cold one.  the trips to town are only twice a month, if that.  i'm usually home, except when i'm down the road working at our new place.  i believe in fenced yards and doggie doors.  i guess the use of the collar will have to be corrective, rather than a training method.
 
is there any advice from members that don't believe in crating?

Certainly no one is trying to force you to go against what you believe in, however, if the wide open (fenced) yard is an issue for your boy, there are alternatives to the crate, such as a dog proofed bathroom.
 
In my experience, cockers are pretty high strung compared to other breeds, and this very much sounds like a sensory overload......

Maybe you#%92ve never heard anything good about the citronella collars, but seriously, shocking your dog for the past two years for doing something that comes naturally to him isn#%92t working either.  Mine activated her citronella collar twice and I haven#%92t used it on her since.  Spritzing a harmless spray in the air in front of them to get their attention as apposed to inflicting pain to their neck seems much more humane to me.  I live in the city, however wouldn#%92t treat my dogs any differently no matter where I lived.  My current two have free run of the house the moment I walk in the door, and although I don#%92t have a doggie door, they go outside to play in a fenced backyard anytime they want, and have oodles of toys to play with to their hearts content.  When I leave my house, I tell them it#%92s time to go to their 24 x 36 x 17 kennel and both of them go running to theirs.  They sit for their liver treat then curl up on their thick soft bed, home-made blanket and snooze with a couple of toys while I#%92m away.  The gates are open on the kennels at all times and my rescue boy goes in his on his own at times to sleep during the day even when I#%92m home.  I have two very calm, friendly and confident cockers.  They know they are loved and adored more than anything in the world.  They bark occasionally, but they are dogs…that#%92s what dogs do.  I let them for a bit, and then tell them quite and they stop.
 
If you truly want to find a solution to help your dog, open your mind to new suggestions.  I firmly believe in fenced yards as well, whether I have a corner lot or 100 acres.  I also believe in doing what is best for them, and making them feel safe and secure.  Leaving them outside unattended when I#%92m not at home is out of the question.  Too many things can happen; first and foremost in my mind is my dogs#%92 welfare.  They can get injured, by something in the yard, another animal or a person passing by.  They also can very easily get stolen.  Mine are kept safely inside my home when I#%92m away, that is a risk I#%92m not willing to take.

so he mostly barks when you're gone-- bark, pause, bark, pause? maybe he's trying to locate you: he barks, waits for your response, none, so he barks again? 
 
and is he barking through the shock collar, or does he only start up again when the batteries run out?
 
re-training dogs that only bark when you're not home is tricky-- you have to rely on the automatic devices, and it sounds like that's not working for you. Also, many cases of non-stop barking when left alone are caused by separation anxiety, a medical condition-- you may need professional help, and medications, if that is the case.
 
I don't understand the comments about crating-- dogs can and do bark like crazy when crated, often more than when not-crated. Being trapped in a tiny cage is not soothing to anxious dogs. Adult dogs are not natural den animals, and getting an eight-year-old dog who has never been crated to accept a crate is going to be quite difficult.

Marlowe was barking in his crate. Not non-stop but enough that we got a nasty note on our door from a neighbor. A crate is not a solution for barking necissarily, but you can keep the dog inside without crating him if you're opposed to that. We solved the problem by confining Marlowe in an area that was safe and dog-proofed but big enough to give him the illusion of freedom.

I agree with everyone else--he's barking outside because there's things to bark at outside and he's likely looking for you (outside, because that is where you went when you left). If I let my dogs go outside when they pleased during the day, there would have been more than one nasty note from neighbors--we would have people showing up at our door with torches and pitchforks. My neighborhood is filled with dogs who, every single moment they are outside, bark nonstop. There's two shelties across the street that, every time they are let out to pee, bark from the second they're let out the door to the second they are coralled back in again. They get mine started if mine are out, without fail.
 
So what you're saying is, you have this dog that barks nonstop when outside, despite a shock collar, and hasn't stopped doing that in two years, yet doing anything to keep the dog from the place where it engages in this behavior is off the table. And in that case, I'm not sure anyone can help you. You're not home to correct the behavior, and you refuse to keep the dog from the area where it feels compelled to engage in the behavior.

Dogs don't need access to the great outdoors 24/7. I know every single person in my neighborhood who's dogs have doggy doors because I can hear them barking all the time, at all hours. Your problem is not unusual and the solution is not brain surgery.