Potty Problem

Our dog, Max, is 16 months old. He was easy to housebreak, but always rather particular about where he "went". We always had problems when we traveled--he just wouldn't go! Not his potty spot.

Two months ago, we moved to a new house. He adjusted pretty well to the new yard and even the leash (we had a fenced yard at the old house). However, the past two weeks, he's decided not to "go". He doesn't want to poo or pee in the yard, on or off the leash. He has held it for 15 hours!

I took him to the vet, and she can find nothing wrong. I even took her a urine sample (what a chore THAT was), but it was fine. Yesterday, he had an accident in the house.

We have one other Doodle who arrived in May, whom Max loves, and an Aussie visitor that's been here since July, whom Max does not love. Any link?

All you doggie psychologists out there--HELP! What is going on with him?? What can I do to get him to potty??