I can understand your frustrations. When I brought Lukas home from the shelter he was great. He was fixed and well his mudes changed. He was very agressive toward some people, and also urinated in the house. On our 52 inch TV no less. It got to the point where I actually had to muzzel him because I was afraid he would bite. TO be honest with you it was alot of work and love. But he had to learn to trust us. These are the steps we took. First we got a crate and re crate trained him. He was thrilled with it but with time it worked. We got a spray bottle with water for when he did mess in the house. We never hit or spanked. Since we didnt know his history we didnt want him to think we were just another person that would hit him. (the vet seemed to think that he was abused) When he had an accident in the house we told him he was bad and give him 1 or 2 sprays and then took him outside. We said lets go out. In a positive voice. When he went outside we praised him. It took almost 2 months to get back on track but it happend.
As for the agression its a scary thing. To be honest I dont know what we did that fixed that. We took him for walks to show him that there were alot of people around when he would Bark or groul we would just tell him NO in a firm voice. Like I said when we had people over if we werent sure we musseld him. He didnt like it but he had to see that people were ok and that there wasnt anything to bark or groul at. The other thing we did was told him to get a toy when someone was comming over. The vet thought it be a good idea to keep his mouth full so giving him a toy worked for us. since his mouth was full he didnt bark and just walked all around and wagged his tail. Becareful with this though. He loves our pillows from the couch, but he always goes to get a toy.
I wont lie to you it was a scary process it was learning experience for us all. Luke is now almost 6 and doing well. He isnt agressive and doesnt bark or groul at anyone. I cant remember the last time he made a mistake in the house.
Things to keep in mind because you dont know his past you never know what he went through. Always be positive recognize his error but praise the positives. Give Lots of love and take for walks. We only used the mussel for about 4 month and only when people came but you need to be able to trust him as much as he needs to trust you!
Best of luck to you! If you have any questions or concerns please dont hesitate to ask!
I hope if nothing else I gave you some confidence. I am new to this site! :)