Help!

In November of last year, we adopted a lab mix (everyone has an opinion what the mix is-maybe sheppard or pit?) He was a year old and about to be put to sleep, and we wanted a large family dog. He had been left by a family whose home had been foreclosed on, and didn't show any signs of problems. Our vet checked him out and said he was excellent in both behavior and health.

After a few months of not knowing how to handle a big dog (he is our first), his behavior began changing. He started jumping, chewing, becoming very hyper and hard to control. We tried Petco training, which did nothing. We began to devote at least 2-4 hours a day with him, thinking maybe he just wasn't getting enough attention. We have a very large yard with plenty of room to roam, so we'd throw the ball outside (and get jumped on), we'd go for walks (and get dragged all over the place), petting, positive reinforcement, etc. We knew from our children that consistency was key, but it didn't seem to matter here--his behavior was just getting worse and we knew we were to blame. We tried kennel training him, but getting him into the kennel was impossible unless my husband was home-the dog is stronger than I am. Just about the only thing that DID work was that at night, we were adamant about him sleeping on his bed, and he would do so easily and throughout the night.

He gained thirty pounds, growing to be a 90lb. dog. At this time, I got pregnant and the jumping got dangerous. We tried a prong collar, which helped some, but still he was so big it was hard to even wrangle him with the collar. He chewed through the wiring to our AC unit in the backyard. We had to do something.

We were at our wits end,when a friend told us about a positive reinforcement "puppy school" that lasted for six weeks. I was leery, but it was held in very high regard, and I could not allow him to jump on me while pregnant. We took him, paid the VERY expensive fee, visited, attended classes with him, and he looked to be much better. When we got him home, we worked very hard to reinforce what we all had learned and for a little while everything was great, then problems started again. He can sit, walk on a leash, and until last week, was not jumping, but he was barking at everything, and began getting up and wondering around the house at night. The "stay" command works for about five minutes, then we fall asleep and get back up.

We were afraid he would chew something up or get into something he shouldn't so we were up all night, correcting him and putting him back on his bed. We've been doing this for two months and we are exhausted. We thought we still weren't spending enough time with him, so now we spend about five hours a day working with him. I don't mind the work, though it's exhausting, but it doesn't appear to be making a difference. What am I doing wrong??