knowlesfamily, it sounds like you have recognized you have a potential timebomb on your hands and are looking for solutions. I would agree with you - you don't want an unpredictable dog on your hands.
One reason may be the dog might not have been adequately socialized. This might be the case if the previous owners were a couple and didn't have many visitors or didn't take the dog out much.
I'll second the advice CanadianK9info gave. I would also add - don't forget about checking our your local library. It's worth looking to see if they have any of the books on dog behaviour. I like the books by Ian Dunbar (creator of Sirius Puppy training method).