Bell Training
My Casey is one year old now, but when we got him last January, he was having trouble with house training also. Someone suggested that we "bell" train him.
We now have a Christmas bell on a string just taped to the wall by the back door, and when he wants to go out, he rings his bell!! It's great. Of course, we now call him a bell abuser, because no sooner than you let him back in, he turns around and rings it again. It is a fun game for him. We have fun too. We also think he's VERY smart.
Good luck in your efforts to house train.