Hi Phillipa
God I know what you're going through!
When we got *Six*, our little Black & Tan Terrier, at 8 wks old last summer I treated her exactly as I would an 8 wk wolfie pup, but boy was it hard work!

She was just like Kai, go out and even watch Bayley wee or poo & then come in and wee.

I spoke to my vet in the end, as she has JRT's, and told her that I was worried I was doing something wrong as it usually only takes a few weeks for a wolfie to work it out, and she just laughed and said that I shouldn't be expecting her to behave like a wolfie and that she wouldn't even think about being clean till she was at least 9 mths! :(
So I just cleaned up, told her off and put her out if I caught her, ignored it when I didn't, and all of a sudden she clicked and started to cry by the back door to go out, she was 8 mths old.
I also had a prob with the fact that she knew she shouldn't do it and sometimes if she did a poo she would eat it, I think it was because if she got caught pooing she got told off so she tried to hide the evidence! So I got some herbal tabs from the pet shop and that stopped, but it was still a long while before she was clean.
Six is 13 months now and is perfect, she spends most of her time on top of a biggie. :D
Sorry I haven't been more helpful with suggestions, but wanted you to know you're not alone! :)
Nicky