I was browsing PetSmart the other day and noticed the Simple Solution "Pee Post." It's a yellow stake you stick in the yard that's treated with hormones (or scents) that encourage the dog to "go" there. It's only $8 on the website, and maybe worth a try, along with everything else.
Good luck! My boy is 1 yr. old now and he still has accidents from time to time. I don't mind so much, partly because we don't have carpet, and if I don't let him out in time, he shouldn't have to hold it!
