You said your 1st 2 doxies trained quickly. How old were they and how long did it take them? Are they completely housebroken, with only a very rare accident?
We got PD at 5 weeks, and started him off on paper. I was able to take him to work, so we (wife and I) were able to take him outside every two hours and praise him. While he was very young, we kept the pads around the house in specific places. When he started missing the Pee pad we stopped those all together. He would plant his front paws on the pad, but not really be aware of where his hind legs were.
At that point, he was a couple of months old, and we converted him to totally outside. Later, we added a doggie door. We've not had an accident since he was 6 months old, I think, if not younger. He is now 8 years old.
We got Henry when he was 6 months old, and I think he was already mostly trained. We were vigilant with him, however, and took him out on the leash in the mornings and evenings. The only accident's we had with Henry were after we made him mad and he'd poop on the floor. A total of three times during the 7 years we had him. His first "pooping" was after we dropped him off at PetSmart to be groomed. He let us know that he didn't like it, and we've never taken him back.
Frank is a 2 year old rescue. We have simply got set in our ways and I think we are being too lazy with him. I think that if I leashed him up and took him outside at least every morning and every evening and took him on walks on a regular basis he would be better behaved. He does pretty good, but will still pee on a rug every now and then.
He also likes to chew on things, he's destroyed two or three doggy beds, several squeaky toys, and has started eating our leather couch. The couch is over 20 years old, and we'll need to get rid of it eventually. He's just helping us overcome our sentimentality about the couch.
Still, its hard not to get excited when we come home and find fluff all over the living room.
We've had Frank for 5 months.