Ignore the size for a minute and the fact that he's docked and the coat texture, color and markings are right straight out of the AKC description of a blue ACD.
And in the United States there is a registry called something like The American Herding Dog Registry. I know this only because a friend of mine got a dog and I stayed with them when I was in California for dog show and we spent quite a lot of time looking at his dogs registration papers and the standard for a blue Heeler. One of the things I noticed on the pedigree was that some of the dogs behind him were dual registered AKC and AHDR--and one in the 4th generation was CKC, AKC and AHDR. The purpose of the registry was to allow mixes and non AKC recognized herders to be registered because they worked like herding dogs. Chuck's dog looked enough like your dog to be his brother. He was bigger than an AKC ACD would be (males 18-20" in AKC) but not as tall as your boy--I didn't measure him but he was probably 22 or 22.5". And he was docked.
The history of the ACD as written as the forepiece to the AKC Standard is interesting mostly because the crosses made to achieve the AKC (and Australian registered similar dog) seem pretty well documented . Blue Heelers seem to have been one of the earlier crosses and were called Blue Heelers in many parts of Australia. But they were known in Queensland as Queensland Heelers or Queensland Blue Heelers. In Australia they are often called any of these names but the registry there is the ACD registry.
I don't see German Shepherd at all as a possible cross--he looks to me to be an oversized ACD or one of the closely related breeds that the "other" registry recognizes.
I know some people in this neck of the woods who have been breeding ACD's for years--their dogs are tough, can be scrappy (they don't take much guff from other dogs) but since the were intended to work in packs, groups or at least pairs as herders they are more tolerant of bunches of dogs than your average working dog would be. (Certainly more so than Dobermans.) They are very trainable if you can work around some pretty hard wired drive to herd things.
So what do you guys think he is?????
I think he's ACD--if he's crossed with anything I'd think it was a cross to something bigger but several generations back. But my Aussie was oversized and about half of the Aussies showing when he was shown were oversized. He was just a hair under 24" and weighed a solid 63 pounds. And when I was back east and going to show back there the first year that Aussies were out of the Misc. class there was an amazing mixture of types --the ASCA Aussies who were working farm dogs were often very small--and the ASCA conformation Aussies tended to be BIG.
He's well behaved on a leash. He was surrendered because the owner said he was attacking their other dog and dragging him around by the neck; no injuries or blood drawn. The shelter thinks the owner may have been misinterpreting his behavior. We're wondering if it might have been too rough play or herding behavior from him, not true aggression. Probably the other dog didn't like it and was kicking up a fuss???
These dogs are supposed to be 'biddable'. Sounds to me pretty much like puppy play not aggression at all. And ACD's play hard. One of the Dobermans as a puppy played horribly rough with my Aussie--talk about dragging dogs around by the neck--the Aussie just took it--it upset me and I've been watching Dobes play too rough with each other and any other dog for years--so the Doberman was always surprised when I yelled at him--the expression on his face was "But Henry doesn't mind--why should you care>"
We do have a problem we didn't expect. The shelter says he lived with cats and he seems fine with our cat, not making eye contact and moving away from the cat if they're face to face. He looks a little wary and slants his head away from the cat, but with no sign of wanting to chase him.
Our cat was always a laid back fellow and bombproof in terms of dealing with all kinds of environments.
Has this cat lived with dogs or was he an addition after you'd lost both dogs?
Sounds like the dog has excellent cat manners.
I had a cat who didn't recognize anything except black and tan Dobes--it took a solid three months for him to get used to and accept that the red puppy I came home with was just a funny colored Doberman. On the other hand he (the cat) was very friendly to the Nubian goat that lived next door (and was slated to be the centerpiece of the BBQ that summer. ) But the goat was black and tan and that was before the red puppy so the cat assumed if it was black and tan it was OK.
So he arches his back, puffs big time and does that cat growl thing--that's what we expected. But he won't leave the dog alone. He follows him around the room, stalks and sometimes attacks him...not just play, but a full fledged claws-out, hissing, etc attack. We had the baby gates fixed so the cat could escape if he needed to, but he won't stay on the other side of the gate! He slides under it, follows the dog around and attacks him if the dog gets within a few feet of him.
How long has the dog been there? This is basically a guess and I'll try to think of things that worked when I had cats that didn't like the dogs that were in the same home. Most of the time the cat got used to the dog over a period of time--took as long as 4 months in the case of one dog--who was so incredibly stupid that he persisted in laying in the doorway to the kitchen next to a big chair with fat arms that my cat liked to sit on. So the cat would be there when the dog came in and sit down right beside the chair the cat was on--my cat would extend all his claws and pop the dog on top of the head. The dog (a Lab mix) would shriek and run away and then slink back and try to sit by the chair--the cat would pop him again.
We're worried the dog will decide to attack back if the cat actually gets to him.
So we put the cat on a leash too when they are in the same room.
So what to do? Right now, we've backed off contact; we're walking the dog outside in the yard and past the sliding door, with the cat able to watch from behind a screen door. And he gets tuna fish there too, while the dog is outside and within view. We're doing the live behind a closed door thing and will also try feeding them on either side, switching territories, beds etc. The room the cat is in is my daughter's office, so she will be spending a good deal of time with him (and I get the dog). Tonight at least, the dog will sleep in my daughter's room with her and the cat will have free run of the house (which the cat is used to at night, because he keeps waking us up if he's allowed in our bedrooms). Anything else you can think off?
Do you think this will calm down?
I'm inclined to think what you are doing will eventually cool things down. Usually I tell people to put the dog in an x-pen so that he can look at the cat but can't harm the cat or try to chase the cat--it's somewhat harder when the positions are reversed and you are trying to protect the dog from the cat.
One of the things that I've used when introducing a new cat to the household wasn't going smoothly was to pick a room and use a Feliway diffuser--the diffuser puts a calming scent in the air and I used it about three different times and it does work on cat x cat encounter and since the dog isn't doing anything except existing it might help your kitty calm down. At least enough to figure out that the dog isn't a threat.
One of our vets had a similar problem--all of her cats had lived with a terrier mix (about the size of a Smooth Fox Terrier) and the dog and the three cats got along just fine--the terrier mix passed away (old age--16 or 17 yo) and her kids wanted another dog (her oldest son who was smarter than all the rest of us told her if she didn't do it soon the cats would forget how to act around a dog--and danged if he wasn't right) so she took the kids to the pound and they picked out a little non-descript dog who was about 1/2 the size of the terrier--the cats had a perfect fit--none of them believed it was a dog and if it was a dog it wasn't THIER dog. She's on vacation right now but when she gets back I'll ask her what they did. I can't remember now.
Good luck with this...