The dog isn't the problem... it's you...
unless you catch the dog and discipline them while they are doing the act of say... chewing the couch.... they don't understand what they are being 'attacked' for... even 30 seconds later is too late.... you just promote confusion and aggression in the dog... you are the aggressor...
Maybe your dog is bored... needs some chew toys... needs some more walks... needs some socialising and obedience training..
WebGizmos idea is excellent... watch Cesar... he is magic with dogs... retrain yourself..contact him if you value your dog..
the love of hoses and sprinklers is common with dogs... my Shepherds always loved them... it's a game..
I have watched shows of American pounds where the dogs are strictly assessed for aggression before they are allowed to go to families and have to pass many tests that might show aggression... including taking a food bowl away from the dog mid eating.. etc.. I gather this dog was assessed before you were allowed to rehome it... so, you need to look at what you are doing wrong...
Young kids should never be left unsupervised with dogs, especially larger dogs... kids have a habit of doing some nasty stuff to dogs, even if they don't realise it being too young, and the dog's patience can run out or it can be merely defending itself.... then.. it's the 'savage dog' attack story... unjustly...
That being said... a pitbull or part pitbull wouldn't be my first choice of dogs with kids... there are too many frequent stories of attacks with these dogs that can do a massive amount of damage.... I would say that in all or most of those cases... the owners are at fault for the treatment of the dogs and not having them properly socialised, restrained or housed... a mistreated pit bull isn't something I'd wish to confront and I don't think these dogs that are bred for pig hunting etc belong in domestic situations.... that being said, I know of quite a few family pit bulls that are just the most gorgeous, friendly, lovable sooks of dogs... and great with children.... like all breeds, you have to have knowledge of the parentage and temperament and know how to be, yourself, the Alpha male of the pack and dominate and train your dog correctly...
Being a long time member of the German Shepherd Dog Club... it was a general agreement... that there was no such thing as a bad dog.. just bad owners... proven many times over with people who would come to us with problem dogs.. it was always the owner...
You need to ask yourself what the dog was like with you and the kids, before you started your misguided disciplining... was there any sign of aggression then?
As a 'noob' with dogs... you have a lot to learn... and each dog is different... start watching Cesar's show as your bible... and perhaps join a local obedience school for some socialising to keep your dog stimulated and for you both to learn... If you have a dog locked up all day while you are at work and it's a young, energetic dog, it is going to find ways to amuse itself and take out it's boredom and frustration... hence, the couch...
If your dog is male, it can be a bit more of a challenge than an easier going bitch... if he is not desexed... you might want to discuss that with your vet... though coming from a pound... I'd like to think that was already done..
If your not serious just ignore this...take the dog back and never consider getting a dog again.
Agree with Web.... if you're going to keep 'practicing' on the dogs 'til you (hopefully/maybe) get it right... don't bother getting another, leave them there to have the chance of an owner who will commit to learning how to treat them, and have a chance at a full life and a loving home...