How should I seal a lag screw through stucco in the side of a house?

I want to anchor a wooden privacy fence to the side of my house by screwing a 2-by-4 to the side of the house first and attaching the fence to that. I'm planning to do it right at the corner, so I should be going into a post or at least a 2-by-4. In general the outside of the house is covered by a plywood shear wall, waterproof paper, chicken wire and stucco. My question is, when I do this, what's the best way to seal the screws/holes against moisture?