The VFX of Marmaduke consisted largely of CG head replacement, done by Rhythm & Hues, CIS, and Cinesite.  Over at FXGuide, they have interviews with all three studios on their contributions and how they built the amazing talking dog.

For the surfing sequence, one of the biggest challenges was achieving the right scale. “That’s always a game between how fast things should move,” said O’Neal. “Everybody usually wants a fast-paced sequence, but almost all of the surfing reference we had was shot in slow motion. It’s a cascading effect because once you start the speed of one thing, that drives the speed of everything else. We ended up having all kinds of challenges – how fast could it go to the camera and still have it feel realistic, how much camera shake can you give it without making it feel like a miniature? How explosive can the white water be to make it look really powerful but doesn’t make it look small because it's going too fast? A lot of it was timing and re-running simulations and checking things.”

via fxguide – visual effects news – Marmaduke.