My bluetick coonhound does the whole sneak off and hide thing too. I think that before we got her, she learned that if she got caught, she got in trouble; therefore, in her mind, don't get caught. Through lots and lots and lots of patience and work, 1-1/2 years later, she usually tells us when she needs to go, but still has some accidents. I'm not sure if she'll ever be 100%, but the important thing is that you pay close attention to when they start sneaking off, and then immediately go for a potty break and don't come in until something happens. This gets very tedious, especially if it's cold or rainy, but does work.

The other behavior where they go in the house within 5 minutes of entering is something I have read about especially in puppies. The reason for the behavior is that they are soooo excited about it being time to come in the house that (like children) they just can't hold it and have to go (even if they just went). My setter mix had a littermate that went to the pound two weeks after adoption for this problem. The solution is supposedly to establish a less exciting home entry routine. Make sure it is always at the same time of day, you always do the same activities when you enter (mine always get fed first when they come in, then we walk one hour later, then it's free time to play, sleep, chew, etc with the TV on).