I would suggest keeping him kenneled every second that he's not in your direct line of vision. That way you'll be more likely to catch him in the act and you'll be able to redirect him. Watch for him to act like he's getting ready to go, then run him outside really quick and, of course, praise him when he does the right thing. I wouldn't let him out of your sight for even a moment until he's caught on. It seems that the more times they go inside the house, the harder they are to train later.

I have heard that Bichons are notoriously hard to housebreak. Just be patient and persistent - and ruthless!